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شائع علم المثلثات >

cos(3x)=4cos(3x)-3cos(x)

الحلّ

cos (3 x) = 4 cos (3 x) - 3 cos (x)

الحلّ

x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn, x = π + 2 πn, x = 2 πn

درجات

x = 9 0^{\circ} + 36 0^{\circ} n, x = 27 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n, x = 0^{\circ} + 36 0^{\circ} n

خطوات الحلّ

cos (3 x) = 4 cos (3 x) - 3 cos (x)

من الطرفين

4 cos (3 x) - 3 cos (x)

اطرح

- 3 cos (3 x) + 3 cos (x) = 0

Rewrite using trig identities

- 3 cos (3 x) + 3 cos (x)

cos (3 x) = 4 cos^{3} (x) - 3 cos (x)

cos (3 x)

Rewrite using trig identities

cos (3 x)

أعد الكتابة كـ

= cos (2 x + x)

cos (s + t) = cos (s) cos (t) - sin (s) sin (t)

:فعّل متطابقة الجمع لزوايا

= cos (2 x) cos (x) - sin (2 x) sin (x)

sin (2 x) = 2 sin (x) cos (x)

:فعّل متطابقة الزاوية المضاعفة

= cos (2 x) cos (x) - 2 sin (x) cos (x) sin (x)

cos (2 x) cos (x) - 2 sin (x) cos (x) sin (x)

بسّط:

cos (x) cos (2 x) - 2 sin^{2} (x) cos (x)

cos (2 x) cos (x) - 2 sin (x) cos (x) sin (x)

2 sin (x) cos (x) sin (x) = 2 sin^{2} (x) cos (x)

2 sin (x) cos (x) sin (x)

a^{b} \cdot a^{c} = a^{b + c}

:فعّل قانون القوى

sin (x) sin (x) = sin^{1 + 1} (x)

= 2 cos (x) sin^{1 + 1} (x)

1 + 1 = 2 :

اجمع الأعداد

= 2 cos (x) sin^{2} (x)

= cos (x) cos (2 x) - 2 sin^{2} (x) cos (x)

= cos (x) cos (2 x) - 2 sin^{2} (x) cos (x)

= cos (x) cos (2 x) - 2 sin^{2} (x) cos (x)

cos (2 x) = 2 cos^{2} (x) - 1

:فعّل متطابقة الزاوية المضاعفة

= (2 cos^{2} (x) - 1) cos (x) - 2 sin^{2} (x) cos (x)

cos^{2} (x) + sin^{2} (x) = 1

:فعّل نطريّة فيتاغوروس

sin^{2} (x) = 1 - cos^{2} (x)

= (2 cos^{2} (x) - 1) cos (x) - 2 (1 - cos^{2} (x)) cos (x)

(2 cos^{2} (x) - 1) cos (x) - 2 (1 - cos^{2} (x)) cos (x)

وسٌع:

4 cos^{3} (x) - 3 cos (x)

(2 cos^{2} (x) - 1) cos (x) - 2 (1 - cos^{2} (x)) cos (x)

= cos (x) (2 cos^{2} (x) - 1) - 2 cos (x) (1 - cos^{2} (x))

cos (x) (2 cos^{2} (x) - 1)

وسٌع:

2 cos^{3} (x) - cos (x)

cos (x) (2 cos^{2} (x) - 1)

a (b - c) = ab - a c

: افتح أقواس بالاستعانة بـ

a = cos (x), b = 2 cos^{2} (x), c = 1

= cos (x) 2 cos^{2} (x) - cos (x) 1

= 2 cos^{2} (x) cos (x) - 1 cos (x)

2 cos^{2} (x) cos (x) - 1 \cdot cos (x)

بسّط:

2 cos^{3} (x) - cos (x)

2 cos^{2} (x) cos (x) - 1 cos (x)

2 cos^{2} (x) cos (x) = 2 cos^{3} (x)

2 cos^{2} (x) cos (x)

a^{b} \cdot a^{c} = a^{b + c}

:فعّل قانون القوى

cos^{2} (x) cos (x) = cos^{2 + 1} (x)

= 2 cos^{2 + 1} (x)

2 + 1 = 3 :

اجمع الأعداد

= 2 cos^{3} (x)

1 \cdot cos (x) = cos (x)

1 cos (x)

1 \cdot cos (x) = cos (x) :

اضرب

= cos (x)

= 2 cos^{3} (x) - cos (x)

= 2 cos^{3} (x) - cos (x)

= 2 cos^{3} (x) - cos (x) - 2 (1 - cos^{2} (x)) cos (x)

- 2 cos (x) (1 - cos^{2} (x))

وسٌع:

- 2 cos (x) + 2 cos^{3} (x)

- 2 cos (x) (1 - cos^{2} (x))

a (b - c) = ab - a c

: افتح أقواس بالاستعانة بـ

a = - 2 cos (x), b = 1, c = cos^{2} (x)

= - 2 cos (x) 1 - (- 2 cos (x)) cos^{2} (x)

فعّل قوانين سالب-موجب

- (- a) = a

= - 2 \cdot 1 cos (x) + 2 cos^{2} (x) cos (x)

- 2 \cdot 1 \cdot cos (x) + 2 cos^{2} (x) cos (x)

بسّط:

- 2 cos (x) + 2 cos^{3} (x)

- 2 \cdot 1 cos (x) + 2 cos^{2} (x) cos (x)

2 \cdot 1 \cdot cos (x) = 2 cos (x)

2 \cdot 1 cos (x)

2 \cdot 1 = 2 :

اضرب الأعداد

= 2 cos (x)

2 cos^{2} (x) cos (x) = 2 cos^{3} (x)

2 cos^{2} (x) cos (x)

a^{b} \cdot a^{c} = a^{b + c}

:فعّل قانون القوى

cos^{2} (x) cos (x) = cos^{2 + 1} (x)

= 2 cos^{2 + 1} (x)

2 + 1 = 3 :

اجمع الأعداد

= 2 cos^{3} (x)

= - 2 cos (x) + 2 cos^{3} (x)

= - 2 cos (x) + 2 cos^{3} (x)

= 2 cos^{3} (x) - cos (x) - 2 cos (x) + 2 cos^{3} (x)

2 cos^{3} (x) - cos (x) - 2 cos (x) + 2 cos^{3} (x)

بسّط:

4 cos^{3} (x) - 3 cos (x)

2 cos^{3} (x) - cos (x) - 2 cos (x) + 2 cos^{3} (x)

جمّع التعابير المتشابهة

= 2 cos^{3} (x) + 2 cos^{3} (x) - cos (x) - 2 cos (x)

2 cos^{3} (x) + 2 cos^{3} (x) = 4 cos^{3} (x) :

اجمع العناصر المتشابهة

= 4 cos^{3} (x) - cos (x) - 2 cos (x)

- cos (x) - 2 cos (x) = - 3 cos (x) :

اجمع العناصر المتشابهة

= 4 cos^{3} (x) - 3 cos (x)

= 4 cos^{3} (x) - 3 cos (x)

= 4 cos^{3} (x) - 3 cos (x)

= - 3 (4 cos^{3} (x) - 3 cos (x)) + 3 cos (x)

- 3 (4 cos^{3} (x) - 3 cos (x)) + 3 cos (x)

بسّط:

- 12 cos^{3} (x) + 12 cos (x)

- 3 (4 cos^{3} (x) - 3 cos (x)) + 3 cos (x)

- 3 (4 cos^{3} (x) - 3 cos (x))

وسٌع:

- 12 cos^{3} (x) + 9 cos (x)

- 3 (4 cos^{3} (x) - 3 cos (x))

a (b - c) = ab - a c

: افتح أقواس بالاستعانة بـ

a = - 3, b = 4 cos^{3} (x), c = 3 cos (x)

= - 3 \cdot 4 cos^{3} (x) - (- 3) \cdot 3 cos (x)

فعّل قوانين سالب-موجب

- (- a) = a

= - 3 \cdot 4 cos^{3} (x) + 3 \cdot 3 cos (x)

- 3 \cdot 4 cos^{3} (x) + 3 \cdot 3 cos (x)

بسّط:

- 12 cos^{3} (x) + 9 cos (x)

- 3 \cdot 4 cos^{3} (x) + 3 \cdot 3 cos (x)

3 \cdot 4 = 12 :

اضرب الأعداد

= - 12 cos^{3} (x) + 3 \cdot 3 cos (x)

3 \cdot 3 = 9 :

اضرب الأعداد

= - 12 cos^{3} (x) + 9 cos (x)

= - 12 cos^{3} (x) + 9 cos (x)

= - 12 cos^{3} (x) + 9 cos (x) + 3 cos (x)

9 cos (x) + 3 cos (x) = 12 cos (x) :

اجمع العناصر المتشابهة

= - 12 cos^{3} (x) + 12 cos (x)

= - 12 cos^{3} (x) + 12 cos (x)

12 cos (x) - 12 cos^{3} (x) = 0

بالاستعانة بطريقة التعويض

12 cos (x) - 12 cos^{3} (x) = 0

cos (x) = u :

على افتراض أنّ

12 u - 12 u^{3} = 0

12 u - 12 u^{3} = 0 : u = 0, u = - 1, u = 1

12 u - 12 u^{3} = 0

12 u - 12 u^{3}

حلّل إلى عوامل:

- 12 u (u + 1) (u - 1)

12 u - 12 u^{3}

- 12 u

قم باخراج العامل المشترك:

- 12 u (u^{2} - 1)

- 12 u^{3} + 12 u

a^{b + c} = a^{b} a^{c}

:فعّل قانون القوى

u^{3} = u^{2} u

= - 12 u^{2} u + 12 u

- 12 u

قم باخراج العامل المشترك

= - 12 u (u^{2} - 1)

= - 12 u (u^{2} - 1)

u^{2} - 1

حلل إلى عوامل:

(u + 1) (u - 1)

u^{2} - 1

1^{2}

كـ

1

اكتب مجددًا

= u^{2} - 1^{2}

x^{2} - y^{2} = (x + y) (x - y)

فعّل قانون فرق المربّعات

u^{2} - 1^{2} = (u + 1) (u - 1)

= (u + 1) (u - 1)

= - 12 u (u + 1) (u - 1)

- 12 u (u + 1) (u - 1) = 0

حلّ عن طريق مساواة العوامل لصفر

u = 0 or u + 1 = 0 or u - 1 = 0

u + 1 = 0

حلّ:

u = - 1

u + 1 = 0

انقل

1

إلى الجانب الأيمن

u + 1 = 0

من الطرفين

1

اطرح

u + 1 - 1 = 0 - 1

بسّط

u = - 1

u = - 1

u - 1 = 0

حلّ:

u = 1

u - 1 = 0

انقل

1

إلى الجانب الأيمن

u - 1 = 0

للطرفين

1

أضف

u - 1 + 1 = 0 + 1

بسّط

u = 1

u = 1

The solutions are

u = 0, u = - 1, u = 1

u = cos (x)

استبدل مجددًا

cos (x) = 0, cos (x) = - 1, cos (x) = 1

cos (x) = 0, cos (x) = - 1, cos (x) = 1

cos (x) = 0 : x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn

cos (x) = 0

cos (x) = 0 :

حلول عامّة لـ

cos (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn

x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn

cos (x) = - 1 : x = π + 2 πn

cos (x) = - 1

cos (x) = - 1 :

حلول عامّة لـ

cos (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

x = π + 2 πn

x = π + 2 πn

cos (x) = 1 : x = 2 πn

cos (x) = 1

cos (x) = 1 :

حلول عامّة لـ

cos (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

x = 0 + 2 πn

x = 0 + 2 πn

x = 0 + 2 πn

حلّ:

x = 2 πn

x = 0 + 2 πn

0 + 2 πn = 2 πn

x = 2 πn

x = 2 πn

وحّد الحلول

x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn, x = π + 2 πn, x = 2 πn

رسم

أمثلة شائعة

8arctan(x)=2pi

8 arctan (x) = 2 π

tan(2x)sin(x)=sin(x)

tan (2 x) sin (x) = sin (x)

sin(u)=-3/5 ,(3pi)/2 <u<2pi

sin (u) = - \frac{3}{5}, \frac{3 π}{2} < u < 2 π

2-2sin^2(x/2)=sin^2(x)

2 - 2 sin^{2} (\frac{x}{2}) = sin^{2} (x)

3cos(B)-1=5cos(B)+1

3 cos (B) - 1 = 5 cos (B) + 1