Сosa-cosb=-2sin(a-b)/2*sin(a+b)/2
cos3a-cos5a=2sinasin4a
(a²+2ab+b²)/ab - (a²-2ab+b²)/ab = 4
(a²+2ab+b²-a²+2ab-b²)/ab = 4ab/ab = 4
наверное так <u>ab-1-ba-1 </u>
1
<u>
</u>
1) = xyz / z(x-y) = xy / x-y
2) = a(x-y) / a(x+y) = x-y / x+y
3) = 3d(c+1) / 3d(2c-1) = c+1 / 2c-1