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# 1 – Cos 2a is equal to ## Cos2a formula

Cos 2a : 1 – cos 2a is equal to what ? There are some important trigonometric identities which are known as double angle formula like Sine 2x, Cosine 2x, Tangent 2x because these trigonometric identities have double angles in them. We will understand this formula through solved examples. Cos 2 A = Cos2A – Sin2A = 2Cos2A – 1 = 1 – 2sin2A

We can easily drive 1 – Cos 2a is equal to 2sin2A formula by using sum formulas of trigonometry. Some formula can be derived by using Pythagorean identities. There are some important addition formulas of trigonometry –

• sin (A + B) = sin A cos B + cos A sin B
• cos (A + B) = cos A cos B – sin A sin B
• tan (A + B) = (tan A + tan B) / (1 – tan A tan B)

## Cos 2a, Sin 2a and Tan 2a Double Angle Formulas

We must know the addition formula of trigonometry cos (A + B) = cos A cos B – sin A sin B to find the 1 – Cos 2a is equal to 2sin2A. In this formula, we will put A = B the formula will become, cos (A + A) = cos A cos A – sin A sin A = cos 2A = cos2A – sin2A.

Now we will use Pythagorean identity sin2A + cos2A = 1 to drive 1 – Cos 2a is equal to 2sin2A formula. We will drive cos 2A formula by using Pythagorean identity sin2A + cos2A = 1. There are two other formulas of cos 2A trigonometric function can be derived as well.

• (i) cos 2A = cos2A − (1 − cos2A) = 2cos2A – 1
• (ii) cos 2A = (1- sin2A) – sin2A = 1 – 2sin2A

By using cos 2A formula = (1- sin2A) – sin2A = 1 – 2sin2A we can find 1 – Cos 2a is equal to 2sin2A formula derivation.

• cos 2A = (1- sin2A) – sin2A = 1 – 2sin2A
• cos 2A = 1 – 2sin2A
• 1 – cos 2A = 2sin2A

Cos 2a formula, Sin 2a and Tan 2a Double Angle Formulas. Please follow this link of Explanation of Mathematics formula – Click

• sin 2A = 2 sin A cos A (or) (2 tan A) / (1 + tan2A)
• cos 2A = cos2A – sin2A (or) 2cos2A – 1 (or) 1 – 2sin2A (or) (1 – tan2A) / (1 + tan2A)
• tan 2A = (2 tan A) / (1 – tan2A)
What is equal to cos 2A?

cos 2A = cos2A – sin2A (or) 2cos2A – 1 (or) 1 – 2sin2A (or) (1 – tan2A) / (1 + tan2A)

Which of the following is equal to sin2A 1 cos2A?

Sin 2A/(1+cos2A)=tanA

How do you find the value of cos 2A?

cos 2A = cos2A – sin2A (or) 2cos2A – 1 (or) 1 – 2sin2A (or) (1 – tan2A) / (1 + tan2A)

What is sin2A equal to?

sin 2A = 2 sin A cos A (or) (2 tan A) / (1 + tan2A)

What is tan 2A?

tan 2A = (2 tan A) / (1 – tan2A)

What is cos 2A sin 2A?

cos2A−sin2A=2cos2A−1

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