17 a C4 2 M An expression is any combination of C1 for explanation of expression letters and numbers, e.g. 3x + 5y. An equation contains an equals sign C1 for explanation of equation and at least one variable, e.g. 3x + 5y = 10. A formula is like an equation, but it is a rule for working out a particular C1 for explanation of formula value, such as the area of a rectangle or the cost of cleaning windows, e.g. A lb, A l = where is area, is length b and is breadth. C1 for explanation of identity An identity looks like a formula but it is true for all values, e.g. b 1)2 x2 (x + = + 2x + 1 x. is true for all values of For example: State whether each item is an expression, equation, formula or C3 C1 for an activity that works identity. Explain why. C1 for plenty of practice x y y A x + 2x + = 6 = πr2 3x = 2x + a C1 for quality of activity m2 m m b = × 5x2 3 – x A bh 10 = 7 = – v ut at2 c = + 10 5t – x2 p = 16 5p = 5 × y x2 v d = 1 = – x2 1 = (x + 1)(x 1) – – 7
17 a b An expression is any combination of letters and numbers, e.g. 3x + 5y. An equation contains an equals sign and at least one variable, e.g. 3x + 5y = 10. A formula is like an equation, but it is a rule for working out a particular value, such as the area of a rectangle or the cost of cleaning windows, e.g. A = lb, where A is area, l is length and b is breadth. An identity looks like a formula but it is true for all values, e.g. (x + 1)2 = x2 + 2x + 1 is true for all values of x. For example: State whether each item is an expression, equation, formula or identity. Explain why. a x + y 2x + y = 6 A = πr2 3x = 2x + x b m2 = m × m 5x2 – 3 10 = x – 7 A = bh c v = ut + at2 10 – 5t x2 = 16 5p = 5 × p d y = x2 – 1 v = x2 – 1 = (x + 1)(x – 1) C4 C3 2 C1 for explanation of expression C1 for explanation of equation C1 for explanation of formula C1 for explanation of identity C1 for an activity that works C1 for plenty of practice C1 for quality of activity M 7