q1- The system of equations y = x^2 − 4x + c and y = −7x + 8 has two solutions, one at
x = 1, and another at x = −4. Find the value of c.
i made the 2 equations equal to each other so
x^2 − 4x + c= −7x + 8
x^2 + 3x -8 +c
sub x=-1 in
so it would be c=4 but then i thought to factorise the equation and use null factor law to find c? Mr F says: Why would you do that? Substitute x = 1 => c = 4. Substitute x = -4 => c = 4. Solved.