Question

Find sin 48 and cos 42 in surd form without using calculator or log books

Answer 1

$\sin(48) = \sin(30 + 18) = \sin(30) \cos(18) + \cos(30) \sin(18)$
we know the values of sin30,cos30
we can also know the values of sin18 ,cos 18 by writing as sin(5×18)=sin90=1
let x=18
and then solve the equation to get sinx which is sin18
also that sin48=cos42