If ab = 9 and a² + b² = 81, then (a+b)² = ?​

99

Step-by-step explanation:

Through some clever algebra, we can combine our first two equations using the fact that

We have the a² and the b² in the equation , and we almost have a 2ab in the equation . To get that 2ab, we can simply double both sides of the first equation to get . From there, we'll add the first two equations together, giving us the summed equation

And since , we can equivalently say that

i belive those are the ones that are under 90 degreese.