What is sin 35° sin55° - cos35° cos55°

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justaguide | College Teacher | (Level 2) Distinguished Educator

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The value of sin 35*sin 55 - cos 35*cos 55 has to be determined. Here it is not necessary to know the values of the sine or cosine of 35 or 55. Instead use the rule: sin a*sin b - cos a*cos b = -cos(a + b)

sin 35*sin 55 - cos 35*cos 55

=> -cos(35 + 55)

=> -cos 90

=> 0

The value of sin 35*sin 55 - cos 35*cos 55 = 0