Substitution Flashcards

All 7 cards in this deck

What are the steps to substitute a value into an expression?

e.g. find $3x + 4$ when $x = 5$

1. Replace the letter with the number in brackets: $3 \times (5) + 4$
2. Apply BIDMAS: $15 + 4$
3. Answer: $19$

When substituting a negative value, how should you write it in the expression?

e.g. $m = -3$ in $4m^2$

In brackets: $4 \times (-3)^2$, so the whole of $-3$ is squared.

True or false? $(-3)^2 = -9$.

False. $(-3)^2 = -3 \times -3 = 9$.

In what order are operations carried out once you have substituted the numbers in?

BIDMAS: brackets, indices, division and multiplication, then addition and subtraction.

True or false? When $x = 4$, $x^3 = 12$.

False. $x^3 = 4 \times 4 \times 4 = 64$; the power means repeated multiplication, not multiply by $3$.

What must you check about the values before substituting into a scientific or real-life formula?

That the units match the ones the formula needs, e.g. convert minutes to hours for a speed in km/h.

In the formula speed $= \dfrac{\text{distance}}{\text{time}}$, what unit does the answer have if distance is in km and time is in hours?

km/h — the distance unit divided by the time unit.