Page 50 - 新思维数学学生用书9 样章

2.6 Deriving and using formulae

Continued Tip

d Can you identify the shapes in parts c i and c ii? Compare your
e Make F the subject of your formula. answers to parts

Work out F when E = 5 and V = 7. c i and c ii with the
What does your value of F tell you? shapes in the last
f Compare and discuss your answers to parts a to e two rows of the
with other pairs in your class. table in part a.

4 Amy is x years old. Ben is 2 years older than Amy.
Alice is six years younger than Amy.
a Write an expression for Ben’s age and Alice’s age in terms of x.

b Write a formula for the total age, T, of Amy, Ben and Alice.
c Use your formula in part b to work out T when x = 19.
d Rearrange your formula in part b to make x the subject.
e Use your formula in part d to work out x when T = 62.

5 Use the formula v = u + at to work out the value of
a v when u = 7, a = 10, t = 8
b v when u = 0, a = 5, t = 25 Tip
c u when v = 75, a = 4, t = 12 In parts c to f start

d u when v = 97, a = 6, t = 8.5 by changing the
e t when v = 80, u = 20, a = 6 subject of the
f a when v = 72, u = 34, t = 19. formula.
6 Adrian buys and sells paintings.

He uses the formula shown to work out the percentage profit he makes.

Percentage profit = selling price − cost price ×100
cost price

Work out Adrian’s percentage profit on each of these paintings.
a Cost price $250, selling price $300
b Cost price $120, selling price $192

c Cost price $480, selling price $1080

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