Mischa wrote the quadratic equation 0=-x2+4x-7 in standard form. if a = -1, what is the value of c in her equation?

For this case we have that by definition, a quadratic equation in its standard form is given by:

In this case we have the following equation:

So, according to the standard form we have:

The value of c is -7.

check above link.

graphically?   well, you graph them both, the solutions is where they both intersect each other, since there are two solutions, meaning they will meet twice, or namely the linear will run into the quadratic curve twice, and where they meet, those x,y coordinates are the solutions to the system.