Question

Упростите выражение. cosa + cos2a + cos6a + cos7a​

Answer 1

cosa + cos2a + cos6a + cos7a

(cosa+cos7a)+(cos2a+cos6a)

2cos4acos3a+2cos4acos2a

2cos4a*(cos3a+cos2a)

2cos4a*2cos(5a/2)cos(a/2)

4cos4a*cos(5a/2)*cos(a/2)