Question

Sin 70 sin 20 - cos 20 cos70

Answer 1

sin 20 = sin(90-70)= cos 70

sin 70= sin(90-20)=cos 20

answer is 0

Answer 2

Answer:

$\red { sin70 sin20 - cos 20 cos 70 }\green {= 0}$

Step-by-step explanation:

$\red { sin70 sin20 - cos 20 cos 70 }$

$= -( cos 20 cos 70 - sin 70 sin20 )$

$= - cos(20+70)$

$\boxed {\pink { cosAcosB - sinA sinB = cos(A+B)}}$

$= - cos 90\degree$

$\green { = 0}$

$\boxed { \pink { cos 90\degree = 0 }}$

Therefore.,

$\red { sin70 sin20 - cos 20 cos 70 }\green {= 0}$

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