For equivalency problems that require the quadratic formula, we still begin by using cross multiplication. However, any cross multiplication that involves multiplying variable terms by other variable terms is likely to result in an expression that can't easily be solved via algebra. In cases like these, you may need to use techniques like factoring and/or the Quadratic Formula. For example, let's look at the equation ((x +1)/3) = (4/(2x - 2)). First, let's cross multiply:  (x + 1) × (2x - 2) = 2x2 + 2x -2x - 2 = 2x2 - 2 4 × 3 = 12 2x2 - 2 = 12. At this point, we want to express this equation in quadratic form (ax2 + bx + c = 0), which we do by setting the equation equal to zero. In this case, we subtract 12 from both sides to get  2x2 - 14 = 0. Some values may equal 0. Though 2x2 - 14 = 0 is the simplest form of our equation, the true quadratic equation is 2x2 + 0x + (-14) = 0. It will probably help early on to mirror the form of the quadratic equation even when some values are 0. The quadratic formula (x = (-b +/- √(b2 - 4ac))/2a)  will help us solve for our value x at this point. Don’t be intimidated by the length of the formula. You’re simply taking the values from your quadratic equation in step two and plugging them into the appropriate spots before solving.  x = (-b +/- √(b2 - 4ac))/2a. In our equation, 2x2 - 14 = 0, a = 2, b = 0, and c = -14. x = (-0 +/- √(02 - 4(2)(-14)))/2(2) x = (+/- √( 0 - -112))/2(2) x = (+/- √(112))/2(2) x = (+/- 10.58/4) x = +/- 2.64 By plugging the calculated value of x back into your quadratic equation from step two, you can easily determine if you reached the correct answer. In this example, you would plug both 2.64 and -2.64 into the original quadratic equation.

How would you rephrase that briefly using Vietnamese?
Nhân chéo hai phân số. Biểu diễn phương trình dưới dạng phương trình bậc hai. Giải phương trình bằng cách thay các hệ số đã biết vào trong công thức nghiệm. Kiểm tra đáp án bằng cách thay giá trị x trở lại vào phương trình bậc hai của bạn.