Question

evaluate cos48 × cos 42 - sin48 × sin42​

Answer 1

Answer:

cos48 .cos42 -sin48. sin42

cos48. cos42 -cos (90-48).cos(90-42)

cos48. cos42 - cos 48. cos 42

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Answer 2

Given ÷

EVALUATE.

Cos48 x cos 42 - Sin 48 x sin 42

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Formulas used

cos (90°-A) => Sin A

sin (90°-A) => cos A

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Solution..-

$\cos(48) \times \cos(42) - \sin(48) \times \sin(42) \\ \\ = > > \frac{ \cos(48) }{ \sin(42) } - \frac{ \sin(48) }{ \cos(42) } \\ \\ = > > \frac{ \cos(48) }{ \ \sin(90 - 42) } - \frac{ \sin(48) }{ \cos(90 - 48) } \\ \\ = > > \frac{ \cos(48) }{ \cos(48) } - \frac{ \sin(48) }{ \sin(48) } \\ \\ = > > 1 - 1 \\ \\ = > > 0$

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Others Formulas related to this...

(1)sin(90°-A)= cosA

(2) Cos(90°-A)= Sin A

(3)tan(90°-A) = cot A

(4)Cot (90°-A)= tanA

(5)Cosec(90°-A)=SecA

(6) Sec(90°-A)= cosec A

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