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A Level Maths Inequality Help!

username3806922

I would really appreciate if anyone could help me out on part (a) and (c) D:

help mee.png

(edited 2 years ago)

Reply 1

mqb2766

Youre told the perimeter inequality for a) so what does that give?

Then can you solve the quadratic (area) inequality and what values of x satisfy both sets of inequalities?

(edited 2 years ago)

Reply 2

username3806922

Original post by mqb2766

Youre told the perimeter inequality for a) so what does that give?

Then can you solve the quadratic inequality and what values of x satisfy both sets of inequalities?

I did (20+x)+(20+x)+x+x < 300, and simplified it to 40+4x<300 but I don't think that's correct :"(

For C I solved my answer to part (b) which was (20+x)(x)>4800 and I got x<-80 and x>60 but in the markscheme it says x=65? I'm not sure where they got 65 from..

Thank you for responding by the way :")

Reply 3

mqb2766

Original post by bluetaetae_12

WHen you simplify the perimeter inequality what do you get? Then combine it with the quadratic ....

What does the mark scheme give as an answer?

(edited 2 years ago)

Reply 4

username3806922

Original post by mqb2766

WHen you simplify the perimeter inequality what do you get? Then combine it with the quadratic ....

What does the mark scheme give as an answer?

Ohh thank you so muchh I got the right answer
I attached the mark scheme below :biggrin:

(edited 2 years ago)

mark.png110.3KB

Reply 5

mqb2766

I got confused when you said =65 in the mark scheme, but their solution is obviously correct.

If you get a bit confused solving inequalities, simply treat them as equalities and solve.
Then use knowledge about the original less than / greater than to flip them back into inequalities.