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Hi there!
The formula to find the are of a circle is :
a = r²
The formula to find the circumference of a circle is :
c = 2r
In order to use the area formula, you need to figure out what the radius (r) is.
If we solve for "r" in the circumference equation, we have :
r = c ÷ (2)
Now we use this to replace "r" in the area formula :
a = ( c ÷ (2
))²
When we simplify this we get :
a = c² ÷ 4
Now you can put your value of "c" into this equation and find "a".
*Remember, is about 3.1416.
Solving for "a" :
a = c² ÷ 4
a = 28² ÷ 4
28² = 28 × 28 = 784
a = 784 ÷ 4
4 = 4 ×
= 12.56637061435917
a = 784 ÷ 12.56637061435917
a = 62.38873769202297cm²
You need to round to the nearest square centimeter, which means that you need to round to the nearest whole number :
a = 62cm²
There you go! I really hope this helped, if there's anything just let me know! :)
m∠1 = 30° (by Vertical angle theorem)
m∠A = 80° (by Triangle sum theorem)
m∠D = 80° (by Triangle sum theorem)
The value of x is 7.5 and y is 9.
Solution:
∠ACB and ∠DCE are vertically opposite angles.
Vertical angle theorem:
<em>If two lines are intersecting, then vertically opposite angles are congruent.</em>
⇒ m∠DCE = m∠ACB
⇒ m∠1 = 30° (by Vertical angle theorem)
In triangle ACD,
Triangle sum property:
<em>Sum of the interior angles of the triangle = 180°</em>
⇒ m∠A + m∠C + m∠B = 180°
⇒ m∠A + 30° + 70° = 180°
⇒ m∠A + 100° = 180°
⇒ m∠A = 100° – 180°
⇒ m∠A = 80° (by Triangle sum theorem)
Similarly, m∠D = 80° (by Triangle sum theorem)
In ΔACD and ΔDCE,
All the angles are congruent, so ΔACD and ΔDCE are similar triangles.
<em>In similar triangle corresponding sides are in the same ratio.</em>
Do cross multiplication.
90 = 12x
7.5 = x
Now, to find y:
Do cross multiplication.
9y = 72
Divide by 9, we get
y = 8
Hence the value of x is 7.5 and y is 9.