bikram57
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if sinA=√3-1/2√2,then prove that cos2A=√3/2 prove that

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VirαtKσhli

Answer:

[tex]\boxed{\sf cos2A =\dfrac{\sqrt3}{2}}[/tex]

Step-by-step explanation:

Here we are given that the value of sinA is √3-1/2√2 , and we need to prove that the value of cos2A is √3/2 .

Given :-

• [tex]\sf\implies sinA =\dfrac{\sqrt3-1}{2\sqrt2}[/tex]

To Prove :-

•[tex]\sf\implies cos2A =\dfrac{\sqrt3}{2} [/tex]

Proof :-

We know that ,

[tex]\sf\implies cos2A = 1 - 2sin^2A [/tex]

Therefore , here substituting the value of sinA , we have ,

[tex]\sf\implies cos2A = 1 - 2\bigg( \dfrac{\sqrt3-1}{2\sqrt2}\bigg)^2 [/tex]

Simplify the whole square ,

[tex]\sf\implies cos2A = 1 -2\times \dfrac{ 3 +1-2\sqrt3}{8} [/tex]

Add the numbers in numerator ,

[tex]\sf\implies cos2A = 1-2\times \dfrac{4-2\sqrt3}{8} [/tex]

Multiply it by 2 ,

[tex]\sf\implies cos2A = 1 - \dfrac{ 4-2\sqrt3}{4} [/tex]

Take out 2 common from the numerator ,

[tex]\sf\implies cos2A = 1-\dfrac{2(2-\sqrt3)}{4} [/tex]

Simplify ,

[tex]\sf\implies cos2A = 1 -\dfrac{ 2-\sqrt3}{2}[/tex]

Subtract the numbers ,

[tex]\sf\implies cos2A = \dfrac{ 2-2+\sqrt3}{2} [/tex]

Simplify,

[tex]\sf\implies \boxed{\pink{\sf cos2A =\dfrac{\sqrt3}{2}} } [/tex]

Hence Proved !

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