CLASS 8 MATHS · ALGEBRAIC EXPRESSIONS AND IDENTITIES

Evaluate algebraic expressions

Replace each variable with its value (in brackets if negative), then follow BODMAS.

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Worked examples

Example 1 · level 1

Find the value of 6x − 10 when x = 5.

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Substitute: 6 × 5 − 10.
Each term: 30 + (−10).
Total = 20.

Answer: 20

Example 2 · level 2

Find the value of −x² + 4x − 10 when x = 5.

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Substitute: −1 × 5² + 4 × 5 − 10.
Each term: (−25) + 20 + (−10).
Total = −15.

Answer: -15

Example 3 · level 3

Find the value of 3x² − xy + 2y² when x = 3 and y = −4.

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Substitute: 3 × 3² − 1 × 3 × (−4) + 2 × (−4)².
Each term: 27 + 12 + 32.
Total = 71.

Answer: 71