<em>Greetings from Brasil...</em>
Be that unknown number X
Then we can write the following expression:
X + 4.7 = 8.1
<h2>X = 3.4</h2>
Answer:
Step-by-step explanation: ok
Trigonometry can be used to find angles and sides of simple triangles. If an 18-foot ladder touches a building 14 feet up the wall then the angle can be deduced by trigonometry. In this case, the ladder defines the hypotenuse (H) of the triangle and the wall defines the opposite (O) side of the triangle. Therefore we can use the equation theta=sin^-1(O/H) . This yields an angle of 51 degrees.
Lizzie has 18 dimes and 12 quarters
<em><u>Solution:</u></em>
Let "d" be the number of dimes
Let "q" be the number of quarters
We know that,
value of 1 dime = $ 0.10
value of 1 quarter = $ 0.25
Given that LIzzie has 30 coins
number of dimes + number of quarters = 30
d + q = 30 ---- eqn 1
Also given that the coins total $ 4.80
number of dimes x value of 1 dime + number of quarters x value of 1 quarter = 4.80

0.1d + 0.25q = 4.8 ------ eqn 2
Let us solve eqn 1 and eqn 2
From eqn 1,
d = 30 - q ---- eqn 3
Substitute eqn 3 in eqn 2
0.1(30 - q) + 0.25q = 4.8
3 - 0.1q + 0.25q = 4.8
0.15q = 1.8
<h3>q = 12</h3>
From eqn 3,
d = 30 - 12
<h3>d = 18</h3>
Thus she has 18 dimes and 12 quarters
<h2>Answer:</h2>
[1] Area of base = 13 × 13 = 169in².
Area of faces = 4 (1/2 × 13 × 8) = 208in².
Surface area = (169 + 208)in² = 377in².
[2] Area of base = 1/2 × 5.2 × 4.5 = 11.7in².
Area of faces = 3 (√3/4 × 5.2²) = 35.1in².
Surface area = (35.1 + 11.7)in² = 46.8in².
[3] Area of base = 7 × 10 = 70in².
Area of faces = 2(1/2 × 7 × 6) + 2(1/2 × 10 × 4.8)
= 98in².
Surface area = (70 + 98)in² = 168in².