Explicație pas cu pas:
a)
[tex]( \sqrt{7} + \sqrt{6} )^{2} = 7 - 6 = 1 \\ ( \sqrt{5} + \sqrt{2} )( \sqrt{5} - \sqrt{2} ) = 5 - 2 = 3 \\ (2a + 5b)^{2} = 4a ^{2} + 25b^{2} [/tex]
[tex]\it a)\ (\sqrt7-\sqrt6)^2=(\sqrt7)^2-2\sqrt7\sqrt6+(\sqrt6)^2=7-2\sqrt{42}+6=13-2\sqrt{42}\\ \\ \\ b)\ (\sqrt5+\sqrt2)(\sqrt5-\sqrt2)=(\sqrt5)^2-(\sqrt2)^2=5-2=3\\ \\ \\ c)\ \ (2a+5b)^2=4a^2+2\cdot2a\cdot5b+25b^2=4a^2+20ab+25b^2[/tex]
