1.

Prove that tan72=tan18+2tan54

Answer» SOLUTION:-

LET,
tan54 = TAN(72-18)

= tan54 =( tan72-tan18)/1+tan72.tan18

= tan54 = ( tan72-tan18)/1+tan(90-18).tan18

= tan54 =( tan72-tan18)/1+cot18.tan18

= tan54 =( tan72-tan18)/2

= tan72-tan18 = 2tan54

=(tan72 = tan18+2tan54)PROVED




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