How can you expand brackets? e.g: (x-4)(x+7)

The answer is of the form ax²+bx+c The a term is found by the product of the coefficients of the x in the brackets. e.g (2x+7)(-4x+6) would give -8x² . However for this example, we will only use coefficients of 1. The coefficient of the x term (b) will be sum of the numbers after the x (e.g: (6x-4)(4x+3)). For the first bracket the b term is -4 and for the second bracket the b term is +3. The product of these numbers is -1, so this is the coefficient of the x term. The c term in the quadratic is the product of these numbers. Using the previous example, -4 x 3 = -12 so this is the c term. Putting these answers into our quadratic give us x²+3x-28.