Question

sinA = cos2A is true when A is equal to

a) 0°
b) 30°
c) 45°
d) 60°
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Answer 1

Answer:

Question is based on trigonometric double angle formula for sin2A=2sinAcosA. As a first step bring all terms to LHS. Therefore, the value of A=0.

a) 0°

Answer 2

Step-by-step explanation:

sin2A=2sinA

⇒2sinAcosA=2sinA

⇒2sinA(cosA−1)=0

⇒sinA=0,cosA−1=0

⇒sinA=0,cosA=1

sinA=0⇒A=0,π,2π

cosA=1⇒A=0,2π

∴A={0,π,2π}∩{0,2π}

={0,2π}

Hence A=0