Question

Find the value of cos75 Cos15​

Answer 1

Ans:

cos 75= cos(45+30) = cos(a+b)=cosa cosb - sin a sin b

cos 45 cos 30 - sin 45 sin 30

1/√2 * √3/2 - 1/√2*1/2

=√3-1/2√2

cos 15 = cos (45-30) = cos(a -b)= cosa cosb + sina sinb

cos45 cos30 + sin 45 sin30

1/√2*√3/2 + 1/√2*1/2

=√3+1/2√2

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Answer 2

Answer:

answer is 1/4

Step-by-step explanation:

• cos75 = (√3-1)/(2√2)

• cos15 =(√3+1)/(2√2)

cos75×cos15

=(√3-1)/(2√2)×(√3+1)/(2√2)

= 3-1/4×2

= 2/8

={1/4}....... final answer

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