Question

Two solutions of the equation Ax+By = 1 are (2, -1) and (-3,-2). Find A and B.

Answer 1

Answer:

Substitute in the values of both given coordinates & form 2 equations:

$\left \{ {{A(2)+B(-1)=1} \atop {A(-3)+B(-2)=1}} \right. \\\\=\left \{ {{2A-B=1} \atop {-3A-2B=1}} \right.$

Find the value of B from the equation 2A - B = 1:

$2A-B=1\\-B=1-2A\\B=2A-1$

Substitute in the B-value to the other equation:

$-3A-2B=1\\-3A-2(2A-1)=1\\-3A-4A+2=1\\-7A=1-2\\-7A=-1\\A=\frac{-1}{-7} =\frac{1}{7}$

Find the B-value using the equation from before:

$B=2A-1=2(\frac{1}{7})-1=\frac{2}{7} -\frac{7}{7} =-\frac{5}{7}$  

Therefore the equation Ax + By = 1 would equal:

$\frac{1}{7} x-\frac{5}{7} y=1$