Difference between revisions of "1989 AHSME Problems/Problem 6"

m (Solution)
m (Solution)
Line 6: Line 6:
  
 
==Solution==
 
==Solution==
Setting <math>y=0</math> we have that the <math>x-</math>intercept of the line is <math>x= / frac {6}{a} </math>. Similarly setting <math>x=0</math> we find the <math>y-</math>intercept to be <math>y=6/b</math>. Then <math>(18/ab)=(1/2)(6/a)(6/b)</math> so that <math>18/ab = 6</math>, simplifying we would get <math>ab=3</math>. Hence the answer is <math>\fbox{A}</math>.
+
Setting <math>y=0</math> we have that the <math>x-</math>intercept of the line is <math>x=6/a </math>. Similarly setting <math>x=0</math> we find the <math>y-</math>intercept to be <math>y=6/b</math>. Then <math>(18/ab)=(1/2)(6/a)(6/b)</math> so that <math>18/ab = 6</math>, simplifying we would get <math>ab=3</math>. Hence the answer is <math>\fbox{A}</math>.
  
 
-minor adjustments by Kevinliu08
 
-minor adjustments by Kevinliu08

Revision as of 01:13, 8 November 2022

Problem

If $a,b>0$ and the triangle in the first quadrant bounded by the co-ordinate axes and the graph of $ax+by=6$ has area 6, then $ab=$

$\mathrm{(A) \ 3 } \qquad \mathrm{(B) \ 6 } \qquad \mathrm{(C) \ 12 } \qquad \mathrm{(D) \ 108 } \qquad \mathrm{(E) \ 432 }$

Solution

Setting $y=0$ we have that the $x-$intercept of the line is $x=6/a$. Similarly setting $x=0$ we find the $y-$intercept to be $y=6/b$. Then $(18/ab)=(1/2)(6/a)(6/b)$ so that $18/ab = 6$, simplifying we would get $ab=3$. Hence the answer is $\fbox{A}$.

-minor adjustments by Kevinliu08

See also

1989 AHSME (ProblemsAnswer KeyResources)
Preceded by
Problem 5
Followed by
Problem 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
All AHSME Problems and Solutions

The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. AMC logo.png