Grade DE Changing the subject Change the subject

Grade D/E Changing the subject Change the subject of a formula If you have any questions regarding these resources or come across any errors, please contact helpful-report@pixl. org. uk

Key Vocabulary Formula Subject Variable Change the subject Make ‘x’ the subject Rearranging formulae

How to change the subject Make x the subject of the formula: (+9) y = x – 9 y + 9 = x x = y + 9 (+9) We normally write x on the LHS

How to change the subject • (+ 3) (÷ 2) x= y+3 2

Change the subject – now you try Equation 5 x + 10 y = 15 7 x – 21 y = 14 23 – 4 x = 12 y 10 y – 5 x = 4 4 y + 2 x = 8 3 x – 2 y = 3 11 x + 22 y = -33 Make x the subject

Change the subject – now you try Equation 5 x + 10 y = 15 7 x – 21 y = 14 23 – 4 x = 12 y Make x the subject x = 3 – 2 y x = 2 + 3 y x = 23 - 3 y 10 y – 5 x = 4 x = 2 y - 4 y + 2 x = 8 3 x – 2 y = 3 x = 4 – 2 y x = 1 + 2 y 11 x + 22 y = -33 a = -3 – 2 y 4 4 5 3

Change the subject – now you try Change the formula to make Distance the subject And Time the subject Change the formula to make Diameter the subject and radius the subject Change the formula to make radius the subject

Change the subject – now you try Change the formula to make Distance the subject And Time the subject Distance = Speed x Time = Distance/Speed Change the formula to make Diameter the subject and radius the subject D = C/π r = C/2 π Change the formula to make radius the subject r = √ (A/ π)

How to change the subject If v 2 = u 2 + 2 as make a the subject of the formula - u 2 ÷ 2 s v 2 = u 2 + 2 as v 2 - u 2 = 2 as v 2 - u 2 a= 2 s - u 2 ÷ 2 s

More Complex Rearranging formula Make x the subject × (3 t + x) + 2 x – 3 ty Factorise 2(y - x ) y = (3 t + x) y(3 t + x) = 2(y - x) 3 ty + xy = 2 y - 2 x xy + 2 x = 2 y - 3 ty x(2 + y)= 2 y - 3 ty ÷ (2+ y) x = 2 y – 3 ty (2 + y) × (3 t + x) Expand Brackets + 2 x – 3 ty

Problem Solving and Reasoning Use the diagram to form as many equations as you can g f g=f+h f=g–h h=g–f h g is the subject f is the subject h is the subject Hint: Substitute in numbers to help check the equations Eg. g = 10 h = 3 f = 7

Reason and explain What is different about questions where there is a power involved? Can you make one up? Explain why rearranging a formula can help you to find the radius of a circle if you know the area of the circle.