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Finding an equation with differentiation or integration help

http://www.examsolutions.net/a-level-maths-papers/Edexcel/Core-Maths/Core-Maths-C1/2014-June/paper.php

Q.10 A.) So initially when i tried to do the question i did DY/DX then put in the (4) as X to find the gradient. After that i did Y-25=M(X-4) and got the wrong answer. I checked and i'm supposed to use integration to find it. Just wondering how o i know when i have to use integration or differentiation on questions like this to find the equation.
If it gives you f'(x), use integration, if f(x) us differentiation. Because f'(x) is the gradient, whilst f(x) is the line
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Avatar for WilliamSlim
WilliamSlim
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Original post by devangdave
If it gives you f'(x), use integration, if f(x) us differentiation. Because f'(x) is the gradient, whilst f(x) is the line

Would that be the case with every question?
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Avatar for gec98
gec98
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Original post by WilliamSlim
http://www.examsolutions.net/a-level-maths-papers/Edexcel/Core-Maths/Core-Maths-C1/2014-June/paper.php

Q.10 A.) So initially when i tried to do the question i did DY/DX then put in the (4) as X to find the gradient. After that i did Y-25=M(X-4) and got the wrong answer. I checked and i'm supposed to use integration to find it. Just wondering how o i know when i have to use integration or differentiation on questions like this to find the equation.


It gives the equation in terms f'(x) which is another way of writing dy/dx, therefore when you have an equation which is already differentiated, in order to find the original equation you will always intergrate it (just remember to do +c on the end as the y intercept depends on the points you've been given). Hope that makes sense!
Original post by WilliamSlim
Would that be the case with every question?



Almost every single one, that I expect you'll come across. Unless they ask for a turning point, then you differentiate f'(x) once, or f(x) twice

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