Найти значение выржания

1) 2b/5a-5a/2b = (4b²-25a²)/10ab 2) (4b²-25a²)/10ab*1/(2b+5a) = (2b+5a)(2b-5a)/10ab(2b+5a) = (2b-5a)/10ab (2*1/9-5*1/5)/10*1/9*1/5 = (2/9-1)/2/9 = -7/9*9/2 = -7/2 = -3,5