Δ= [tex] b^{2} [/tex] - 4ac = [tex]( -7)^{2} [/tex] + 4*2*15 = 49 + 120 = 169 = [tex] 13^{2} [/tex]
[tex] x_{1,2} [/tex] = [tex] \frac{-b+- \sqrt{delta} }{2a}[/tex] = [tex] \frac{7+-7}{2*2} [/tex] = [tex] \frac{7+-7}{4} [/tex]
[tex] x_{1} [/tex] = [tex] \frac{7+7}{4} [/tex] = [tex] \frac{14}{4} [/tex] = [tex] \frac{7}{2} [/tex]
[tex] x_{2} [/tex] = [tex] \frac{7-7}{4} [/tex] = [tex] \frac{0}{4} [/tex] = 0
Dar problema ne spune ca solutia este numar pozitiv (strict mai mare ca 0) asa ca [tex] x_{2} [/tex] nu convine.
S: x= [tex] \frac{7}{2} [/tex]
