Chapter 1.2, Problem 6E

Which of the following are true? Assume that x and y are fixed real numbers.
(a) Triangles have three sides iff squares have four sides.
(b) $\text{7}+\text{5}=\text{12}$ if and only if $\text{1}+\text{1}=\text{2}$ .
(c) $\text{5}+\text{6}=\text{6}+\text{5}$ iff $\text{7}+\text{1}=\text{1}0$ .
(d) A parallelogram has three sides iff 27 is prime.
(e) The Eiffel Tower is in Paris if and only if the chemical symbol forhelium is H.
(f) $\sqrt{10}+\sqrt{13}<\sqrt{11}+\sqrt{12}$ iff $\sqrt{13}-\sqrt{12}<\sqrt{11}-\sqrt{10}$ .
(g) $x^{\text{2}}\ge 0$ if and only if $x\ge 0$ .
(h) $x^{\text{2}}-y^{\text{2}}=0$ iff $(x-y)(x+y)=0$ .
(i) $x^{\text{2}}+y^{\text{2}}=\text{5}0$ if and only if ${(x+y)}^{\text{2}}=\text{5}0$ .