Answer:
A. 
Step-by-step explanation:
According to tangent theorem, a tangent is formed when the radius of a circle is perpendicular to the line, meeting at a point around the circle, such that the tangent line would be perpendicular to the radius of the circle with a center.
Given that 
is a tangent of the circle O, at a point C, and 
is a radius, therefore, it follows that:
.
This means the radius of the circle is perpendicular to the tangent formed at point C.
The third choice, 4x²+18x+0.25=0, is correct.
The frame will have the same thickness on both sides of the mirror. Therefore we add 5+x+x to get the total length, and we have 4+x+x to get the total width.
The area is found by multiplying the total width and total length:
A=(5+x+x)(4+x+x)
A=(5+2x)(4+2x)
Multiplying the binomials, we have:
A=5*4+5*2x+2x*4+2x*2x
A=20+10x+8x+4x²
A=20+18x+4x²
We know that the area is 19.75:
19.75=20+18x+4x²
We need quadratics set equal to 0, so subtract 19.75 from each side:
19.75-19.75 = 20+18x+4x²-19.75
0=0.25+18x+4x²
In standard form, it will be:
4x²+18x+0.25=0
The volume of a rectangular pyramid = 1/3 ×Area×height
=1/3×L×W×H
if the dimensions were doubled
therefore,
V=1/3 × (9×2)×(14×2)×(10×2)
=1/3×18×28×20
=3360 cubic centimetres
