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3 years ago

Please help im so confused?

Mathematics

1 answer:

Setler79 [48]3 years ago

4 0

Surface area = PI x rL + PI x r^2

since the answer is in terms of PI, remove PI from the equation:

surface are = rl +r^2

r = 3 and l = 15

3*15 + 3^2 = 45 +9 = 54

answer is 54PI units^2

Answer is C

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Write the formula for the parabola.

Talja [164]

Answer:

Given the focus (h,k) and the directrix y=mx+b, the equation for a parabola is (y - mx - b)^2 / (m^2 +1) = (x - h)^2 + (y - k)^2.

Step-by-step explanation:

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3 years ago

The temperature went from -16°F to 7°F. What was the change in temperature?

worty [1.4K]

Answer:

To find this out, we first need to see the change, is it a positive change or a negative change? Well in this case, as the temperature is increasing, we find that the change is positive. The next step we need to do, id that, how much was the change by, we can find this out by finding the absolute value of the difference of -16°F and 7°F

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2 years ago

Please help with 2 Math questions. I dont really understand

lisabon 2012 [21]

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3 years ago

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krok68 [10]

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Step-by-step explanation:

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3 years ago

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Oduvanchick [21]

Answer:

A), B) and D) are true

Step-by-step explanation:

A) We can prove it as follows:

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B) When you compute the product Ax, the i-th component is the matrix of the i-th column of A with x, denote this by Ai x. Then, we have that $||Ax||=\sqrt{(A_1 x)^2+\cdots (A_n x)^2}$ . Now, the colums of A are orthonormal so we have that (Ai x)^2=x_i^2. Then $||Ax||=\sqrt{(x_1)^2+\cdots (x_n)^2}=||x||$ .

C) Consider $S=\{(0,2),(2,0)\}\subseteq \mathbb{R}^2$ . This set is orthogonal because $(0,2)\cdot(2,0)=0(2)+2(0)=0$ , but S is not orthonormal because the norm of (0,2) is 2≠1.

D) Let A be an orthogonal matrix in $\mathbb{R}^n$ . Then the columns of A form an orthonormal set. We have that $A^{-1}=A^t$ . To see this, note than the component $b_{ij}$ of the product $A^t A$ is the dot product of the i-th row of $A^t$ and the jth row of $A$ . But the i-th row of $A^t$ is equal to the i-th column of $A$ . If i≠j, this product is equal to 0 (orthogonality) and if i=j this product is equal to 1 (the columns are unit vectors), then $A^t A=I$

E) Consider S={e_1,0}. S is orthogonal but is not linearly independent, because 0∈S.

In fact, every orthogonal set in R^n without zero vectors is linearly independent. Take a orthogonal set $\{u_1,u_2\cdots u_p\}$ and suppose that there are coefficients a_i such that $a_1u_1+a_2u_2\cdots a_nu_n=0$ . For any i, take the dot product with u_i in both sides of the equation. All product are zero except u_i·u_i=||u_i||. Then $a_i||u_i||=0$ then $a_i=0$ .

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3 years ago