Evaluate- cos- 20-circ- cos- 70-circ- - sin- 20-circ- sin- 70-circ-

Question

Toppr Admin · Accepted Answer

Cos20-xB0-cos70-xB0-x2212-sin70-xB0-sin20-xB0-0-x21D2-cos20-xB0-cos70-xB0-x2212-sin70-xB0-sin20-xB0-cos-70-xB0-20-xB0-x2235-cosAcosB-x2212-sinAsinB-cos-A-B-cos90-xB0-0Hence- the answer is solved-

Evaluate: $cos 20^{\circ} cos 70^{\circ} - sin 20^{\circ} sin 70^{\circ}$

$cos 20 ° cos 70 ° - sin 70 ° sin 20 ° = 0$

$\Rightarrow cos 20 ° cos 70 ° - sin 70 ° sin 20 °$

$= cos (70 ° + 20 °) [∵ cos A cos B - sin A sin B = cos (A + B)]$

$= cos 90 °$

$= 0$

Hence, the answer is solved.

Evaluate: cos20∘cos70∘−sin20∘sin70∘

cos20°cos70°−sin70°sin20°=0⇒cos20°cos70°−sin70°sin20°=cos(70°+20°)[∵cosAcosB−sinAsinB=cos(A+B)]=cos90°=0Hence, the answer is solved.

Evaluate: $cos 20^{\circ} cos 70^{\circ} - sin 20^{\circ} sin 70^{\circ}$

$cos 20 ° cos 70 ° - sin 70 ° sin 20 ° = 0$

$\Rightarrow cos 20 ° cos 70 ° - sin 70 ° sin 20 °$

$= cos (70 ° + 20 °) [∵ cos A cos B - sin A sin B = cos (A + B)]$

$= cos 90 °$

$= 0$

Hence, the answer is solved.