Question

X (в квадрате)+ax-15=0 ,если x1=3

Answer 1

${x}^{2} + ax - 15 = 0 \\ x_{1} = 3 \\ {3}^{2} + a \times 3 - 15 = 0 \\ 3a + 9 - 15 = 0 \\ 3a = 6 \\ a = 2$
${x}^{2} + 2x - 15 = 0 \\ x_{1} + x_{2} = - 2 \\ 3 + x_{2} = - 2 \\ x_{2} = - 2 - 3 \\ x_{2} = - 5$