Question

Aflați nr x și y
(2•x plus 3) •(2•xplus4) =56

Answer 1

    
$(2x+3)(2x+4)=56 \\ 4 x^{2} +6x+8x+12 = 56 \\ 4 x^{2} +14x+12 = 56 \\ 4 x^{2} +14x+12-56 = 0 \\ 4 x^{2} +14x-44 = 0\;\;|:2 \\ 2 x^{2} +7x-22 = 0 \\ \\ x_{12}= \frac{-7 \pm \sqrt{49+4 \cdot 2 \cdot 22} }{2 \cdot 2} = \frac{-7 \pm \sqrt{225} }{4}= \frac{-7 \pm 15 }{4} \\ \\ x_1=\frac{-7 + 15 }{4}= \frac{8}{4}= \boxed{2}\\\\ x_2 = \frac{-7 - 15 }{4}= \frac{-22}{4}= \boxed{- \frac{11}{2}} = \boxed{-5,5}$