# Video: GCSE Mathematics Foundation Tier Pack 2 β’ Paper 2 β’ Question 24

GCSE Mathematics Foundation Tier Pack 2 β’ Paper 2 β’ Question 24

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### Video Transcript

Given the following information, find the value of π§. π§ is equal to π₯ squared minus nine π¦. π₯ is equal to four. π¦ is equal to negative five.

So looking at the information weβve been given, weβve been given an expression for π§ in terms of π₯ and π¦. π§ is equal to π₯ squared minus nine π¦. Weβve also been given the values of π₯ and π¦. To work out the value of π§, we just need to substitute the numeric or number values of π₯ and π¦ into the algebraic expression for π§.

So substituting four for π₯ and negative five for π¦, we have that π§ is equal to four squared minus nine multiplied by negative five. Now, we do have a calculator to help with this. So we can type the calculation into our calculator exactly as itβs written on screen. And the value that the calculator will return is 61.

However, we could also work this out ourselves. Firstly, we have four squared, which remember means four multiplied by four. And four multiplied by four is 16. Then, we have nine multiplied by negative five. Now, nine multiplied by five is 45. And as we have a positive number multiplied by a negative number, this will give a negative answer overall. So nine multiplied by negative five is negative 45.

Our calculation for π§ then has become 16 minus negative 45. Next, we just need to remember that these two minus signs next to each other will make a positive. So our expression becomes 16 plus 45. 16 plus 45 is indeed equal to 61. So we found the value of π§.