Answer:
A
Step-by-step explanation:
The line from the vertex to the base is a perpendicular bisector and divides the isosceles triangle into 2 right triangles.
Using Pythagoras' identity in either of the 2 right triangles, then
([tex]\frac{1}{2}[/tex] x )² + 3² = ([tex]\sqrt{45}[/tex] )²
[tex]\frac{1}{4}[/tex] x² + 9 = 45 ( subtract 9 from both sides )
[tex]\frac{1}{4}[/tex] x² = 36 ( multiply both sides by 4 to clear the fraction )
x² = 144 ( take the square root of both sides )
x = [tex]\sqrt{144}[/tex] = 12 → A
