Hello, didn't know exactly where to post this. Any guidance would be much appreciated. Thanks.

Leta,b, and cbe integers andx,y and zbe real numbers. Use the technique of working backward from the desired conclusion to prove that

a). [(x+y)/2] ≥(greater than or equal to) (sqrt)√(x*y)

b.) If x^3 + 2*x^2 < 0 , then 2*x + 5 < 11

c). If an isoceles triangle has sides of length x,y and z, where x=y and z=(sqrt)√(2*x*y), then it is right triangle