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If x = 3 and y = -1, then 3x2 + 2xy - 5 = ? A: 18 B: 24 C: 12 D: 16

iris [78.8K]

$x = 3 , \ y = -1 \\ \\ 3x^2 + 2xy - 5 = 3\cdot 3^2 + 2\cdot 3\cdot (-1)-5=\\ \\=3\cdot 9 -6-5=27-11=16 \\ \\ Answer : \ D: \ \ 16$

8 0

3 years ago

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Help meez 40 pts use surface area formula of cylinder that is for Lateral surface area and for total surface area

jeka94

Answer:So the radius of the cylinder is 2.65 cm.

A cylinder can be defined as a solid figure that is bound by a curved surface and two flat surfaces. The surface area of a cylinder can be found by breaking it down into 2 parts:

1. The two circles that make up the caps of the cylinder.

2. The side of the cylinder, which when "unrolled" is a rectangle.

The area of each end cap can be found from the radius r of the circle, which is given by:

A = πr2

Thus the total area of the caps is 2πr2.

The area of a rectangle is given by:

A = height × width

The width is the height h of the cylinder, and the length is the distance around the end circles, or in other words the perimeter/circumference of the base/top circle and is given by:

P = 2πr

Thus the rectangle's area is rewritten as:

A = 2πr × h

Combining these parts together we will have the total surface area of a cylinder, and the final formula is given by:

A = 2πr2 + 2πrh

where:

π is Pi, approximately 3.142

r is the radius of the cylinder

h height of the cylinder

By factoring 2πr from each term we can simplify the formula to:

A = 2πr(r + h)

The lateral surface area of a cylinder is simply given by: LSA = 2πr × h.

Example 1: Find the surface area of a cylinder with a radius of 4 cm, and a height of 3 cm.

Solution:

SA = 2 × π × r2 + 2 × π × r × h

SA = 2 × 3.14 × 42 + 2 × 3.14 × 4 × 3

SA = 6.28 × 16 + 6.28 × 12

SA = 100.48 + 75.36

SA = 175.84

Surface area = 175.84 cm2

Example 2: Find the surface area of the cylinder with a radius of 5.5cm and height of 10cm.

Solution:

The radius of cylinder = 5.5 cm.

The height of cylinder = 10 cm.

The total surface area of the cylinder is therefore:

TSA = 2πr(r+h)

TSA = 11π (5.5+10)

TSA = 170.5 π

TSA = 535.6 cm2

Example 3: Find the total surface area of a cylindrical tin of radius 17 cm and height 3 cm.

Solution:

Again as in the previous example:

TSA = 2πr(r+h)

TSA = 2π× 17(17+3)

TSA = 2π×17×20

TSA = 2136.56 cm2

Example 4: Find the surface area of the cylinder with radius of 6 cm and height of 9 cm.

Solution:

The radius of cylinder: r = 6 cm

The height of cylinder: h = 9 cm

Total surface area of cylinder is therefore:

TSA = 2πr(r + h)

TSA = 12π (6+9)

TSA = 180 π

TSA = 565.56 cm2

Example 5: Find the radius of cylinder whose lateral surface area is 150 cm2 and its height is 9 cm.

Solution:

Lateral surface area of cylinder is given by:

LSA = 2πrh

Given that:

LSA = 150cm2

h = 9cm

π is the constant and its value = 3.14

Substitute the values in the formula and find the value of r by isolating it from the equation:

LSA = 2πrh

150 = 2× π × r × 9

r = 150 / (2×9× π)

r = 2.65cm

So the radius of the cylinder is 2.65 cm.

5 0

1 year ago

10. 2x + 7y = 1 2x - 4y = 12 Solve for y

adoni [48]

Answer:

The solution for y = -1.

Step-by-step explanation:

Given:

$2x\ +\ 7y\ =\ 1$ ....(1)

$2x\ -\ 4y\ =\ 12$ ....(2)

So, to solve for y, first we solve for x in equation (2):

$2x-4y=12$

⇒ $2x=12+4y$

Dividing both sides by 2,

⇒ $x=6+2y$

Now, substituting the value of x in equation (1):

$2x+7y=1$

⇒ $2(6+2y)+7y=1$

⇒ $12+4y+7y=1$

⇒ $12+11y=1$

⇒ $11y=1-12$

⇒ $11y=-11$

Dividing both sides by 11,

⇒ $y=-1$

Therefore, the solution for y = -1.

7 0

2 years ago

what positive number satisfies the condition that twice the number minus three times the reciprocal of the number is equal to 1?

marshall27 [118]

Solve:

"twice the number minus three times the reciprocal of the number is equal to 1."
3(1)
Let the number be n. Then 2n - ------- = 1
n

Mult all 3 terms by n to elim. the fractions:

2n^2 - 3 = n. Rearranging this, we get 2n^2 - n - 3 = 0.

We need to find the roots (zeros or solutions) of this quadratic equation.

Here a=2, b= -1 and c= -3. Let's find the discriminant b^2-4ac first:

disc. = (-1)^2 - 4(2)(-3) = 1 + 24 = 25.

That's good, because 25 is a perfect square.
-(-1) plus or minus 5 1 plus or minus 5
Then x = ------------------------------ = --------------------------
2(2) 4

x could be 6/4 = 3/2, or -5/4.

You must check both answers in the original equation. If the equation is true for one or the other or for both, then you have found one or more solutions.

8 0

3 years ago

Janeel has a 10-inch by 12-inch photograph. She wants to scan the photograph, then reduce the result

Vaselesa [24]

Complete Question:

Janeel has a 10 inch by 12 inch photograph. She wants to scan the photograph, then reduce the results by the same amount in each dimension to post on her Web site. Janeel wants the area of the image to be one eight of the original photograph. Write an equation to represent the area of the reduced image. Find the dimensions of the reduced image.

Correct Answer:

A) $(10-x)(12-x)=15$