# Thread: can figure out how to do this

1. ## can figure out how to do this

a+b=4
ab=7.74

solve for a and b

any help would really be appreciated.

2. Originally Posted by cherrybomb21
a+b=4
ab=7.74

solve for a and b
Hello,

$a+b=4~\implies~b=4-a$ . Plug in this term into the 2nd equation:

$a(4-a)=7.74$ and solve for a.

But be careful: This equation has no real solution!

3. Hello, cherrybomb21!

Is there a typo?
. . There are no real solutions.

Solve for $a$ and $b\!:\;\;\begin{array}{ccc}a+b &= & 4\\
ab & =& 7.74\end{array}$

Solve the first equation for $b\!:\;\;b \:=\:4-a$

Substitute into the second equation: . $a(4-a) \:=\:7.74$

And we have a quadratic equation: . $a^2 - 4a + 7.74 \:=\:0$

. . which has complex roots: . $\begin{array}{ccc}a & = & 2 \pm i\sqrt{3.74} \\ b & = & 2 \mp i\sqrt{3.74}\end{array}$