SOLUTION: if a, b belong to R+ such that {{{system(a*sqrt(a) + b*sqrt(b) = 183, a*sqrt(b) + b*sqrt(a) = 182)}}} then {{{(9/5)(a + b )= "?"}}}

Algebra ->  Graphs -> SOLUTION: if a, b belong to R+ such that {{{system(a*sqrt(a) + b*sqrt(b) = 183, a*sqrt(b) + b*sqrt(a) = 182)}}} then {{{(9/5)(a + b )= "?"}}}      Log On


   



Question 1141270: if a, b belong to R+ such that

then %289%2F5%29%28a+%2B+b+%29=+%22%3F%22

Answer by Edwin McCravy(20064) About Me  (Show Source):
You can put this solution on YOUR website!
System 1:      

Let x=sqrt%28a%29, x%5E2=a,  y=sqrt%28b%29, y%5E2=b, then

system%28x%5E2%2Ax+%2B+y%5E2%2Ay+=+183%2C+%0D%0A+x%5E2%2Ay+%2B+y%5E2%2Ax+=+182%29

System 2:     system%28x%5E3+%2B+y%5E3+=+183%2C+%0D%0A+x%5E2%2Ay+%2B+x%2Ay%5E2+=+182%29

Multiply the 2nd equation by 3

system%28x%5E2%2Ax+%2B+y%5E2%2Ay+=+183%2C+%0D%0A+3x%5E2%2Ay+%2B+3y%5E2%2Ax+=+546%29

Add the two equations:

x%5E3%2B3x%5E2%2Ay%2B3x%2Ay%5E2%2By%5E3=729

Factor the left side:
 
%28x%2By%29%5E3=729

Take cube roots of both sides:

Eq. 1     x%2By=9

Factor the left side of the 1st equation in system 2

x%5E3+%2B+y%5E3+=+183
%28x%2By%29%28x%5E2-xy%2By%5E2%29=183

Use Eq. 1 to substitute 9 for (x+y)

9%28x%5E2-xy%2By%5E2%29=183
x%5E2-xy%2By%5E2=183%2F9, reduce 183/9 to 61/3

Eq. 2     x%5E2-xy%2By%5E2=61%2F3

Square both sides of Eq. 1:

%28x%2By%29%5E2=9

Eq. 3     x%5E2%2B2xy%2By%5E2=81

Multiply Eq. 2 by -1 and add Eq. 3

%22%22-x%5E2%2Bxy-y%5E2=-61%2F3
 x%5E2%2B2xy%2By%5E2=81

3xy=-61%2F3%2B81
3xy=-61%2F3%2B243%2F3
3xy=182%2F3
xy=182%2F9

Substitute 182%2F9 for xy in in Eq. 2

x%5E2-182%2F9%2By%5E2=183%2F9

x%5E2%2By%5E2=183%2F9%2B182%2F9

x%5E2%2By%5E2=365%2F9

Since x²=a and y²=b,

a%2Bb=365%2F9

expr%289%2F5%29%28a%2Bb%29=%289%2F5%29%28365%2F9%29+=+73

Edwin