We have
sin 72
= 2 cos 36 sin 36 using sin 2A formula
= 2 cos 36 ( 2 sin 18 cos 18) using sin 2A formula again
= 4 cos 36 sin 18 sin 72 as cos18 = sin(90-18) = sin 72
= 2 cos 36 sin 36 using sin 2A formula
= 2 cos 36 ( 2 sin 18 cos 18) using sin 2A formula again
= 4 cos 36 sin 18 sin 72 as cos18 = sin(90-18) = sin 72
or
4 cos 36 sin 18 = 1
2 comments:
Its not much clear to understand
each step is explained clearly. which step is not clear to understand
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