Printable · GCSE Foundation · ages 14-16

Identities, equivalence and algebraic proof worksheet — GCSE Foundation

Fifteen questions on "identities, equivalence and algebraic proof" — DfE statement A6. Print it, or print three versions so neighbours cannot copy by letter; the key gives the letter for each version.

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Identities, equivalence and algebraic proof worksheet — GCSE Foundation

Maths · GCSE Foundation · A6 · Identities, equivalence and algebraic proof · 15 questions

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1.A student is asked whether 3(x − 4) = 3x − 4 is an identity. Which statement gives the correct verdict and reason?
(a)It is an identity, because both sides begin with the term 3x, so they must be equivalent.
(b)It is not even an ordinary equation with a solution: expanding the left-hand side gives 3x − 12, and 3x − 12 = 3x − 4 would require −12 = −4, which is never true.
(c)It is not an identity, because the student forgot to multiply the 4 by 3 on both sides of the equation.
(d)It is not an identity, because the student needs to substitute a specific value of x before comparing the two sides.
2.Which of these is an identity?
(a)2(3x + 1) = 6x + 2
(b)5x + 1 = 5(x + 1)
(c)7 − x = x − 7
(d)4x − 3 = 3x + 5
3.Which of these equations is true for every value of x, making it an identity rather than an equation with just one solution?
(a)5x − 3 = 12
(b)2(x + 3) = 2x + 6
(c)x + 7 = 15
(d)3x = x + 10
4.An equation has exactly one value of x that makes it true, but an identity is true for every value of x. Which of these best explains why 3x + 5 = 20 is an equation rather than an identity?
(a)It has an = sign, and equations always use =.
(b)3x + 5 cannot be simplified, so it must be an equation.
(c)Only x = 5 satisfies 3x + 5 = 20, not every value of x.
(d)A number on the right-hand side makes it an equation.
5.Which expression is equivalent to 7x − 3(2x − 6)?
(a)13x − 18
(b)x − 18
(c)x + 18
(d)x + 6
6.Which expression is equivalent to 6x − (2x − 5)?
(a)8x + 5
(b)8x − 5
(c)4x − 5
(d)4x + 5
7.Which expression is equivalent to 5x − (x + 3)?
(a)4x + 3
(b)6x − 3
(c)4x − 3
(d)5x − 3
8.Two expressions are 4(x + 3) and 4x + 3. A student checks whether they are equivalent by substituting x = 2. Which statement correctly interprets the result?
(a)4(x + 3) = 20 and 4x + 3 = 11 when x = 2, so the two expressions are not equivalent, because the bracket means the 3 must be added before multiplying by 4.
(b)4(x + 3) = 11 and 4x + 3 = 11 when x = 2, since the bracket has no effect on the multiplication, so the two expressions are equivalent.
(c)4(x + 3) = 20 and 4x + 3 = 11 when x = 2, but the two expressions are equivalent because both involve the same terms, 4x and 3.
(d)4(x + 3) = 20 and 4x + 3 = 11 when x = 2, so the two expressions are not equivalent, but they would become equal for some larger value of x.
9.Which expression is equivalent to 2(x + 6)?
(a)2x + 8
(b)x + 12
(c)2x + 12
(d)2x + 6
10.Which expression is equivalent to 3(2x − 5) + 4x?
(a)10x + 15
(b)6x − 15
(c)10x − 15
(d)10x − 5
11.Two expressions are 6(x − 1) and 6x − 6. A student says these are equivalent for every value of x. Is the student correct?
(a)Yes, but only when x is a whole number.
(b)No, since 6(x − 1) means 6x − 1.
(c)No, brackets always change an expression's value.
(d)Yes, since expanding 6(x − 1) gives 6x − 6.
12.A student says that 5(x + 2) is equivalent to 5x + 2. Which statement explains why the student is wrong?
(a)Addition must always be done before multiplication, so 5(x + 2) equals 5x + 10 only when x = 0.
(b)The bracket must be worked out first using a value of x, so the two expressions can only be compared once x is known.
(c)The 5 must multiply both terms inside the bracket, so 5(x + 2) expands to 5x + 10, which is never equal to 5x + 2 for any value of x.
(d)5(x + 2) means 5 × x + 2, so the student's answer of 5x + 2 is actually correct.
13.A student says that (x + 4)² is equivalent to x² + 16. For which value of x do the two expressions give the SAME result, making it look (misleadingly) like the student could be right?
(a)x = 4
(b)x = −4
(c)x = 0
(d)x = 8
14.A market stall's cost of hiring n tables is modelled by two formulas: Formula A: C = 3(2n + 5); Formula B: C = 6n + 15, where C is in pounds. A stallholder says the two formulas always give the same cost. Work out the cost given by each formula when n = 4, and use your results to decide whether the stallholder is correct.
(a)Formula A gives £39 and Formula B gives £39, but the stallholder is wrong because the two formulas use a different number of terms.
(b)Formula A gives £29 and Formula B gives £39, so the stallholder is wrong.
(c)Formula A gives £39 and Formula B gives £39, but this is only true when n = 4, so the stallholder is wrong.
(d)Formula A gives £39 and Formula B gives £39, and since 3(2n + 5) expands to 6n + 15 for every value of n, the stallholder is correct.
15.Which expression is equivalent to 3(x + 4) − 2(x − 1)?
(a)x + 14
(b)x + 10
(c)5x + 10
(d)x + 13

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