### 12X12 Example 9

Substitute the values for the variables you know. Only r is left, so try to isolate r. Subtract 1 from both sides to isolate r on the right. You now have two equations, one using 1.

Simplifying the two equations gives two solutions to the equation. The interest rate is 0. The Simplifying the radical gives. You forgot the negative square root when you took the square root of both sides. Applying the Square Root Property gives. Note that both the positive and negative square roots are included; this is the other probable mistake. Perfect Square Trinomials. Of course, quadratic equations often will not come in the format of the examples above.

Most of them will have x terms. However, you may be able to factor the expression into a squared binomial—and if not, you can still use squared binomials to help you. They are binomials, two terms, that are squared. If you expand these, you get a perfect square trinomial.

Notice that the first and last terms are squares r 2 and 1.

The middle term is twice the product of the square roots of the first and last terms, the square roots are r and 1, and the middle term is 2 r 1. First notice that the x 2 term and the constant term are both perfect squares. Then notice that the middle term ignoring the sign is twice the product of the square roots of the other terms.

In this case, the middle term is subtracted, so subtract r and s and square it to get r — s 2. You can use the procedure in this next example to help you solve equations where you identify perfect square trinomials, even if the equation is not set equal to 0. Notice, however, that the x 2 and constant terms on the left are both perfect squares: 2 x 2 and 5 2.

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Check the middle term: is it 2 2 x 5? Now you can use the Square Root Property. Some additional steps are needed to isolate x.

Simplify the radical when possible. Try it—can you think of two numbers whose product is 68 and whose sum is 20? Completing the Square. One way to solve quadratic equations is by completing the square.

Now let's make this rectangle into a square. First, divide the red rectangle with area bx into two equal rectangles each with area. Then rotate and reposition one of them. You haven't changed the size of the red area—it still adds up to bx.

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The red rectangles now make up two sides of a square, shown in white. The area of that square is the length of the red rectangles squared, or. Here comes the cool part—do you see that when the white square is added to the blue and red regions, the whole shape is also now a square? In other words, you've "completed the square!

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Notice that the area of this square can be written as a squared binomial:. Finding a Value that will Complete the Square in an Expression. The expression becomes. To complete the square, add. Check that the result is a perfect square trinomial. When you complete the square, you are always adding a positive value. Use completing the square to find the value to add that makes x 2 — 12 x a perfect square trinomial.

Then write the expression as the square of a binomial. The correct answer is x — 6 2. The value to add has been calculated correctly:. Note also, that the number you add will always be positive because it is the square of a number.

Solving a Quadratic Equation using Completing the Square. You can use completing the square to help you solve a quadratic equation that cannot be solved by factoring. In the example below, notice that completing the square will result in adding a number to both sides of the equation—you have to do this in order to keep both sides equal!

This equation has a constant of 8. Ignore it for now and focus on the x 2 and x terms on the left side of the equation. This is an equation, though, so you must add the same number to the right side as well. Check that the left side is a perfect square trinomial. Can you see that completing the square in an equation is very similar to completing the square in an expression?

Since you cannot factor the trinomial on the left side, you will use completing the square to solve the equation. Identify b. The same as adding the number to itself. It ends in either 0 or 5. Now, notice how the "ones" place goes down: 9,8,7,6,? And at the same time, the "tens" place goes up: 1,2,3,? Well, your hands can help! Example: to multiply 9 by 8: hold your 8th finger down, and you can count "7" and "2" I often have to say in my mind:. While it is generally more important to know why things work, with the tables I recommend pure memory , it makes future math work much easier. Much like walking, you don't want to think what your feet are doing, you want to enjoy the adventure. I also have a longer list of multiplication tips and tricks if you are interested.

And if you are really good, see if you can beat the high scores at Reaction Math. Hide Ads About Ads.