We have the formula for the area of the triangle as:
[tex]A=\frac{1}{2}\cdot b\cdot h[/tex]If h and b are functions of x, we can replace them in the area function and have the area in function of x:
[tex]\begin{gathered} h=3x^2 \\ b=6x^2+5x \end{gathered}[/tex][tex]\begin{gathered} A=\frac{1}{2}\cdot b\cdot h \\ A=\frac{1}{2}(6x^2+5x)(3x^2) \\ A=\frac{1}{2}(18x^4+15x^3) \\ A=9x^4+\frac{15}{2}x^3 \end{gathered}[/tex]Answer: A = 9*x^4 + (15/2)*x^3
