Đơn giản các biểu thức sau: (cos^2)25 độ-(cos^2)35 độ+(cos^2)45 độ-(cos^2)55 độ+(cos^2)65 độ
Giải thích
d) cos2250-cos2350+cos2450-cos2550+cos2650
=cos2250-cos2350+cos2450-sin2350+sin2250
=cos2250+sin2250-cos2350+sin2350+cos2450
= 1 - 1 + 1/2
= 1/2
d) cos2250-cos2350+cos2450-cos2550+cos2650
=cos2250-cos2350+cos2450-sin2350+sin2250
=cos2250+sin2250-cos2350+sin2350+cos2450
= 1 - 1 + 1/2
= 1/2