a) -1/2*(-2/3)*(-3/4)*(-4/5) = 1/5
1) -1/2 * (-2/3) = 1/2 * 2/3 = (1*2)/(2*3) = 1/3
2) 1/3 * (-3/4) = - (1*3)/(3*4) = -1/4
3) -1/4 * (-4/5) = 1/4 * 4/5 = (1*4)/(4*5) = 1/5
б) -10/11*(-11/12)*(-12/13)*(-13/14)*(-14/15) = -2/3
1) -10/11 * (-11/12) = 10/11 * 11/12 = (10*11)/(11*12) = 10/12 = 5/6
2) 5/6 * (-12/13) = -(5*12)/(6*13) = -(5*2)/(1*13) = -10/13
3) -10/13 * (-13/14) = 10/13 * 13*14 = (10*13)/(13*14) = 10/14 = 5/7
4) 5/7 * (-14/15) = -(5*14)/(7*15) = -(1*2)/(1*3) = -2/3