Learn how to evaluate expressions by substituting variables and perform the required calculations.
About This Lesson
From the lesson
, you know that a variable is used to represent a certain number.
Therefore, you can evaluate an expression by substituting the each variable in the expression with its given number and perform the required calculations. This lesson shows you how.
Remember to include brackets around the substituted variable. These brackets help to minimize calculation mistakes.
It is better to substitute the variables in the expression one at a time. You can substitute the variables all at once when you are more familiarized with the steps involved.
Now, watch the following math video to know more.
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Math Video Transcript
00:00:02.230 In the lesson ' Algebra Variables', we learn that variable can be used to represent a certain number. 00:00:09.090 Therefore, we can evaluate an algebraic expression by substituting each variable with a given number and perform the required calculation. 00:00:18.190 This lesson shows you how. 00:00:23.160 Let's evaluate the expression when p =3, and r = -2. 00:00:29.170 For this expression, only variable p is present. So, substituting p with 3. 00:00:38.070 Remember to always put brackets around the substituted number. This is to minimize mistakes. 00:00:45.030 Now, multiply 2 with 3. this gives 6. next, Add 6 with 2. This gives 8 . Therefore, The evaluated expression is 8. 00:01:01.040 Now, let's evaluate 4p + 3r. We can start by substituting p with 3. 00:01:09.230 Next, multiply 4 with 3. This gives 12. 00:01:16.010 Now, substitute r = -2. multiply 3 with -2. This gives -6. 00:01:26.230 Minus 12 with 6. This gives the answer 6. 00:01:33.150 Next example, p the power of 3, minus 2r square, minus 2. 00:01:40.050 Let's start by substituting r with -2. Now, -2 square is equals to -2 multiply by -2, which is equals to 4. 00:01:56.010 Next, we multiply -2 with 4. This gives -8. 00:02:02.090 Now, by adding -8 and -2, we get -10. 00:02:09.050 Let's substitute p with 3. Now, 3 power of 3 is equals to, 3 * 3 * 3. This gives 27. 00:02:26.080 Alright, the final answer is 27 minus 10, which is 17. 00:02:34.030 One final example, let's evaluate r square minus 2pr. Substituting r with negative 2. 00:02:45.030 Now, negative two to the power of 2 is equals to, -2 multiply by -2. This gives 4. 00:02:56.220 Let's substitute p with 3. -2 multiply by 3 gives negative 6. 00:03:08.120 Now, substitute r with -2. 00:03:13.130 Multiply -6 with -2 gives +12. 00:03:19.110 Now add 4 with +12. The answer is 16. 00:03:25.190 Alright, that's all for this lesson. Try out the practice questions to better your understanding.
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Multiple Choice Questions (MCQ)
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