Question

sin^2 20° + sin^2 70° - tan^2 45°

Answer 1

sin(sq) 20 + sin(sq) 70 - tan(sq) 45

= sin(sq)20 + sin(sq) [90 - 20] - (1) sq [tan 45 = 1]

= sin(sq)20 + cos(sq) 20 - 1 [sin(sq)[90 - A] = cos(sq)A]

= 1 - 1 [Identity: sin(sq)A + cos(sq)A = 1]

= 0

so the ans is 0

Answer 2

${ \sin }^{2}20 \\ = { \sin }^{2} (90 - 70) \\ = { \cos}^{2} 70$
${ \cos }^{2} 70 + { \sin }^{2} 70 = 1$
$as \: { \sin}^{2} \alpha + { \cos}^{2} \alpha = 1$
Substituting this value in the equation
$1 - { \tan }^{2} 45 \\ = 1 - 1 \\ = 0$