Substituting into Formulae
Substitute numerical values into formulae and expressions including scientific formulae; evaluate expressions by replacing variables with given values and computing the result using correct order of operations
What a learner can do afterwards
- Substitute positive and negative values into algebraic expressions and evaluate
- Substitute values into formulae involving multiple operations and powers
- Use correct order of operations when evaluating expressions after substitution
1 · Read
Substitution replaces letters with given numbers. Use the same value every time a letter occurs. In 3x, the 3 multiplies x; it does not join its digits. Put brackets around a substituted negative value. For sums, add the substituted numbers. To add two negatives, add their sizes and keep the minus sign. Adding a positive number moves right on a number line.
A square's area is A = s². With s = 4, A = 4 × 4 = 16. In 4t², only t is squared. With t = 5, calculate 4 × 5² = 4 × 25 = 100. Brackets change this: (4t)² squares the whole product, giving (4 × 5)² = 400. In 4t² + 6, add 6 after calculating the square and product.
After substitution, work inside brackets first, starting with the innermost pair. Within each group, calculate powers, then multiplication and division from left to right, then addition and subtraction from left to right. Multiplication and division have equal priority. Addition and subtraction also have equal priority. The notation x^2 means x², and x^3 means x³.
For 3x + 7 with x = -4, write 3 × (-4) + 7. A positive number times a negative number gives a negative answer: 3 × (-4) = -12. Then -12 + 7 = -5. Subtracting a positive number from a negative number moves farther below zero.
A square uses two copies of its base: with t = -5, t² = (-5) × (-5) = 25. A cube uses three copies: t³ = 25 × (-5) = -125. Two negative factors give a positive product. A positive times a negative gives a negative product. Subtracting a negative adds its opposite: 8 - (-5) = 8 + 5 = 13.
The value of -b is the opposite of b. If b = 5, then -b = -5. Brackets show what a power covers. In (ab)², multiply a and b, then square their product. In ab², square b, then multiply by a. For (a² - b²) ÷ (c + d), calculate each bracket separately before dividing. The divisor must not be zero.
For a triangle, A = b × h ÷ 2, where b is the base and h is the perpendicular height. With b = 8 cm and h = 3 cm, A = 8 × 3 ÷ 2 = 12 cm². Replace both letters, multiply, then divide by 2.
Swap each letter for its number, then follow the order of operations to find the answer.
The lesson, questions and flashcards were written for this dataset.
Three questions were written for this dataset. Seven questions are adapted from Portland Community College WeBWorK materials credited to Alex Jordan, Carl Yao and Chris Hughes. The terms for the retained source records have not been verified.
2 · Watch
به انگلیسیTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
18 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.