This will not only introduce elementary students to geometry, but also begin the complicated thinking associated with algebraic concepts. Using the formula to plug in the known degrees and then find the x is the beginning of much more abstract algebraic thinking.
Handout
Circles rule our lives and have rules of their own! Each circle measures to 350 degrees, and with this knowledge we can begin to find unknown angles!
If a circle measures 360, that means that a half circle measures half -- 180 degrees. In a half circle, there are many different angle combinations. But, we know that they all equal out to 180 degrees.
Knowing this, we can find the great unknown!
Well, we know that the total of the two angles equals 180 degrees. Therefore, angle 1 = angle 2 = 180 degrees.
Let's just plug the numbers into the equation.
63 + x = 180.
The first step is to isolate the variable, in this case the x. We do this by getting rid of the 63 on the left side...
How? Well 63 is a positive number, so the equation really reads
+63 + x = 180.
This means that the opposite of +63 will get rid of that 63, and leave the x by itself. Therefore we subtract 63 from the left side of the equal sign. But there is a gold rule to math: whatever we do to one side, we MUST do to the other. Therefore we MUST also subtract 63 from 180 to balance the scale.
+63 + x = 180
- 63-63
0 + x = 117
So, x = 117 degrees.
Show me your mastery!!!
1.
What degree is x?
2.
What degree is x?
Answer Key
1.
x +45=180
-45 -45
x+0 = 135
x=135
135 degrees
2.
125+x=180
-125 -125
0+x=55
x=55
55 degrees
References
National Council of Teachers of Mathematics [NCTM]. (1989). Curriculum and…
