Question

if tantheta = b/a , then value of cos2theta is what in terms of a and b?
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Answer 1

Answer:

opt3

Step-by-step explanation:

cos^2¤ = 1/sec^2¤= 1/(1+tan^2¤) = 1/(1+(b/a)^2)

1/(a^2+b^2)/a^2

= a^2/(a^2+b^2)---eq1

so sin^2¤= 1/cosec^2¤ = 1/(1+cot^2¤)

so sin^2¤ = 1/1/(1+(a/b)^2)

= b^2/(a^2+b^2)---eq2

and we know that cos2¤ = cos(¤+¤)= cos^2¤-sin^2¤

so from eq1 and eq2

cos2¤= a^2/(a^2+b^2) -b^2/(a^2+b^2)

= (a^2-b^2)/(a^2+b^2)