Question

Prove that, tan70 =tan20+2tan50
2 . Prove that,
(sinX)3 × sin3X +(cosX)3 × cos3X =(cos2X)3

Answer 1

Answer:

tan70=tan(20+50)

tan70 = (tan20+tan50)/(1-tan20tan50)

tan70-tan20tan50tan70 = tan20+tan50

And, [ tan70tan20 = tan70cot70 = 1 ]

so,

tan70-tan50 = tan20+tan50

tan70 = tan20+2tan50 ( proved)