Separate the vectors into their <em>x</em>- and <em>y</em>-components. Let <em>u</em> be the vector on the right and <em>v</em> the vector on the left, so that
<em>u</em> = 4 cos(45°) <em>x</em> + 4 sin(45°) <em>y</em>
<em>v</em> = 2 cos(135°) <em>x</em> + 2 sin(135°) <em>y</em>
where <em>x</em> and <em>y</em> denote the unit vectors in the <em>x</em> and <em>y</em> directions.
Then the sum is
<em>u</em> + <em>v</em> = (4 cos(45°) + 2 cos(135°)) <em>x</em> + (4 sin(45°) + 2 sin(135°)) <em>y</em>
and its magnitude is
||<em>u</em> + <em>v</em>|| = √((4 cos(45°) + 2 cos(135°))² + (4 sin(45°) + 2 sin(135°))²)
… = √(16 cos²(45°) + 16 cos(45°) cos(135°) + 4 cos²(135°) + 16 sin²(45°) + 16 sin(45°) sin(135°) + 4 sin²(135°))
… = √(16 (cos²(45°) + sin²(45°)) + 16 (cos(45°) cos(135°) + sin(45°) sin(135°)) + 4 (cos²(135°) + sin²(135°)))
… = √(16 + 16 cos(135° - 45°) + 4)
… = √(20 + 16 cos(90°))
… = √20 = 2√5
Age of Jen is 13.6 years old
<em><u>Solution:</u></em>
Let "x" be the age of Jack and "y" be the age of Jen
Given that This Christmas, your brother Jack will be 2 years from being twice as old as your sister Jen
The above sentence can be written mathematically as:
Jack age + 2 = twice of age of Jen
The sum of Jacks age and three times Jen's age is 66
Jack age + three times Jen age = 66
x + 3y = 66 ---- eqn 2
Substitute eqn 1 in eqn 2
2y - 2 + 3y = 66
5y - 2 = 66
5y = 68
<h3>y = 13.6</h3>
Thus age of Jen is 13.6 years old
25/5 as a mixed number would be 5.
Let's analyse each option:
A.
Spending money means the money will decrease, so it would be represented by minus 32.
B.
Dropping a rock means its height will decrease, so minus 32 would fit better.
C.
The speed is decreasing, so minus 32 as well.
D.
The amount of books is increasing, so positive 32 fits better in this situation.
Therefore the correct option is D.
