The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

9a - 5a = 4a

You need to find the value of a so solve the first equation in terms of z:

a + z = 9
z = 9 - a

then substitute the result (9 - 1a) into the second equation:

9a - 4(9 - a) = -4
9a + (-4 x 9) + (-4 x -a) = -4
9a - 36 + 4a = -4
9a + 4a = -4 + 36
13a = 32
a = \( \frac{32}{13} \)
a = 2\(\frac{6}{13}\)

A cylinder is a solid figure with straight parallel sides and a circular or oval cross section with a radius (r) and a height (h). The volume of a cylinder is π r²h and the surface area is 2(π r²) + 2π rh.

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).