Question

Cos420°=

Tg(-60°)=

(1-sin^2t)(1+tg^2)=1

Answer 1

$cos 420 = cos (2n + 60^{0}) = cos 60^{0}= frac{ 1 }{2}$
$tg (-60)= - tg60=- sqrt{3}$
$(1-sin^{2}t) (1+tg^{2}t)=1$
$(sin^{2}t+cos^{2}t-sin^{2}t) ( frac{1}{cos^{2}} )=1$
$( frac{cos^{2}}{cos^{2}} )=1$
1=1