Question

determine y para que os pontos A(3,5), B (-3,8) e c ( 4,y) sejam colineares ( estejam na mesma reta).

Answer 1

$Det \left[\begin{array}{ccc}3&5&1\\-3&8&1\\4&y&1\end{array}\right]=0 \\ (1.8.4)+(1.y.3)+(5.-3+1)-(3.8.1)-(5.1.4)-(-3.y.1)=0\\ 32+3y-15-24-20+3y=0\\ 6y+32-59=0\\ 6y-27=0\\ 6y=27\\ y= \frac{27}{6} \\ y= \frac{9}{2}$