Video Transcript
Determine the values of 𝑥 and 𝑦
that maximise the function 𝑝 equals five 𝑥 plus two 𝑦. Write your answer as a point 𝑥,
𝑦.
We’ve been given a region which
represents a series of inequalities. The topmost horizontal inequality
is 𝑦 is less than or equal to eight. The vertical inequality is 𝑥 is
less than or equal to seven. The region is also bound by the
𝑥-axis. So 𝑦 must be greater than or equal
to zero. And finally, we have a diagonal
line with a 𝑦-intercept at eight and a gradient of negative eight over three.
This inequality is, therefore, 𝑦
is greater than or equal to negative eight over three 𝑥 plus eight. All maxima and minima occur at the
corners of the region. We’re specifically interested in
the maximum of the function. So by finding the value of 𝑥 and
𝑦 at these points, we can determine which order pair when substituted into 𝑝
equals five 𝑥 plus two 𝑦 will give us the largest possible value for 𝑝.
Our vertices fall at seven, zero;
seven, eight; zero, eight; and three, zero. At zero, eight, 𝑝 is equal to five
times zero, add two times eight, which gives us a value of 16. At three, zero, 𝑝 is equal to five
times three, add two times zero, which is 15. At seven, eight, 𝑝 is equal to
five times seven, add two times eight, which is 51. And at seven, zero, 𝑝 is equal to
five times seven, add two times zero, which is 35.
Our function 𝑝 equals five 𝑥 plus
two 𝑦 is therefore greatest when 𝑥 equals seven and 𝑦 equals eight. The values of 𝑥 and 𝑦 that
maximise our function are seven, eight.
