Question

Решите уравнение : (20-у) (7-у)=0

Answer 1

$(20-y)(7-y)=0$
$140-20y-7y+ y^{2} =0$
$y^{2} -27y+140=0$
$D= (-27)^{2} -4*1*140=729-560=169$
$x_{1} = \frac{27+ \sqrt{169} }{2} = \frac{27+13}{2} = \frac{40}{2} =20$
$x_{2} = \frac{27-13}{2} =7$