29.01.2013 Views

Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Sec. 14] F<strong>in</strong>d<strong>in</strong>g the Greatest and Smallest Values of Functions 227<br />

2030. Determ<strong>in</strong>e the greatest value of the function z=l+x + 2y<br />

<strong>in</strong> the regions: a) x>0, y^*0, x + y^l\ b)<br />

2031. Determ<strong>in</strong>e the greatest and smallest values of the func-<br />

<strong>in</strong> the region x?+y 2<br />

*^l.<br />

2032. Determ<strong>in</strong>e the greatest and smallest values of the func-<br />

tions a) z = x*y and b) z = #* y 2<br />

tion z = s<strong>in</strong>x-h s<strong>in</strong> y-f- s<strong>in</strong> (x + y) <strong>in</strong> the region O^jt^-2.-<br />

2033. Determ<strong>in</strong>e the greatest and smallest values of the function<br />

z = x' + y* 3xy <strong>in</strong> the region 0^x^2, 1 ^<br />

Sec. 14. F<strong>in</strong>d<strong>in</strong>g the Greatest and Smallest Values of Functions<br />

Example t. It is required to break up a positive number a <strong>in</strong>to three<br />

nonnegative numbers so that their product should be the greatest possible.<br />

Solution. Let the desired numbers be x, y, a x //. We seek the maximum<br />

of the function / (x, y) xy(a x y).<br />

Accord<strong>in</strong>g to the problem, the function / (x, y) is considered <strong>in</strong>side a<br />

closed triangle x^O, y^zQ, x + y^a (Fig. 71).<br />

Solv<strong>in</strong>g the system of equations<br />

f'(x,<br />

Fig. 71<br />

we will have the unique stationary po<strong>in</strong>t (-TTI T j<br />

triangle. Let us test the sufficiency conditions. We have<br />

^or * ne<br />

> (/) = 20, f (x, y)=a2x2y, f" (x, /) =<br />

IXIf yy'<br />

of the

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!