All ACT Math Resources
Example Questions
Example Question #1 : How To Find The Length Of The Side Of Of An Acute / Obtuse Isosceles Triangle
A triangle has a perimeter of inches with one side of length
inches. If the remaining two sides have lengths in a ratio of
, what is length of the shortest side of the triangle?
The answer is .
Since we know that the permieter is inches and one side is
inches, it can be determined that the remaining two sides must combine to be
inches. The ratio of the remaining two sides is
which means 3 parts : 4 parts or 7 parts combined. We can then set up the equation
, and divide both sides by
which means
. The ratio of the remaining side lengths then becomes
or
. We now know the 3 side lengths are
.
is the shortest side and thus the answer.
Example Question #2 : How To Find The Length Of The Side Of Of An Acute / Obtuse Isosceles Triangle
In the standard coordinate plane, the points
and
form two vertices of an isosceles triangle. Which of the following points could be the third vertex?
To form an isosceles triangle here, we need to create a third vertex whose coordinate is between
and
. If a vertex is placed at
, the distance from
to this point will be
. The distance from
to this point will be the same.
Example Question #175 : Triangles
Note: Figure is not drawn to scale.
In the figure above, points are collinear and
is a right angle. If
and
is
, what is
?
Because is isosceles,
equals
or
.
We know that add up to
, so
must equal
or
.
Example Question #231 : Act Math
A light beam of pure white light is aimed horizontally at a prism, which splits the light into two streams that diverge at a angle. The split beams each travel exactly
from the prism before striking two optic sensors (one for each beam).
What is the distance, in feet, between the two sensors?
Round your final answer to the nearest tenth. Do not round until then.
This problem can be solved when one realizes that the light beam's split has resulted in an acute isosceles triangle. The triangle as stated has two sides of feet apiece, which meets the requirement for isosceles triangles, and having one angle of
at the vertex where the two congruent sides meet means the other two angles must be
and
. The missing side connecting the two sensors, therefore, is opposite the
angle.
Since we know at least two angles and at least one side of our triangle, we can use the Law of Sines to calculate the remainder. The Law of Sines says that for any triangle with angles and
and opposite sides
and
:
.
Plugging in one of our angles (and its corresponding
ft side) into this equation, as well as our
angle (and its corresponding unknown side) into this equation gives us:
Next, cross-multiply:
--->
Now simplify and solve:
Rounding, we see our missing side is long.
All ACT Math Resources
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