Hi, Mart.
This equation has an x2 in it, so it is a quadratic equation. If we move the terms around to the standard form, it would be: (Note that I subtracted the 10 to set the equation equal to zero).
-x2 + x + 42 = 0
There are 3 ways to solve this kind of quadratic equation: factoring, completing the square, and the quadratic formula.
Since you didn't specify that you had to use a certain method, I am going to factor it. Since the first term is -x2, the factors have to start with x and -x.
(-x )(x ) = 0
Since the 3rd term is positive, both signs will be the same. Since the middle term is also positive, both signs would be positive.
(x + )(-x + ) = 0
Remember we now have to find a pair of factors for the 3rd term that add or subtract to the coefficient of the 2nd. That is, a pair of factors of 42 that add or subtract to 1.
42 = 7 * 6, and 7 - 6 = 1, so now put 6 and 7 into the equation so that it works out correctly:
(x + 6)(-x + 7) = 0
Since the factors multiply to zero, one of the factors has to be equal to zero:
x + 6 = 0 or -x + 7 = 0
Solving these gives you x = -6 or x = 7.
Hope this helps!