Mathematics Grade 9 15 min

Multiply polynomials to find area

Multiply polynomials to find area

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Introduction & Learning Objectives

Learning Objectives Represent the dimensions of a geometric shape using polynomials. Apply the distributive property and FOIL method to multiply binomials representing length and width. Calculate the area of rectangles and squares with polynomial side lengths. Simplify the resulting polynomial expression for the area into standard form. Evaluate the area of a shape for a given value of the variable. Set up and solve problems involving the area of combined or subtracted geometric shapes, such as a frame around a picture. Ever wondered how a landscape architect plans a garden with a decorative border of a specific width? 🌷 They use algebra to find the exact area for soil or pavers! In this tutorial, we will bridge the gap between abstract algebra and concrete geometry. You w...
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Key Concepts & Vocabulary

TermDefinitionExample PolynomialAn algebraic expression consisting of variables and coefficients, involving only the operations of addition, subtraction, multiplication, and non-negative integer exponents of variables.The expression `4x^2 - 7x + 1` is a polynomial. BinomialA polynomial with exactly two terms.The expression `(x + 9)` is a binomial representing the length of a side. AreaThe measure of the space inside a two-dimensional figure, expressed in square units.A rectangle with length 10 cm and width 4 cm has an area of 40 cm². Distributive PropertyA property stating that multiplying a sum by a number is the same as multiplying each addend by the number and then adding the products.`x(2x + 3) = x(2x) + x(3) = 2x^2 + 3x` FOIL MethodA mnemonic for multiplying two binomials, standing f...
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Core Formulas

Area of a Rectangle A = l \times w To find the area (A) of a rectangle, you multiply its length (l) by its width (w). When the dimensions are represented by polynomials, this operation becomes polynomial multiplication. The Distributive Property a(b + c) = ab + ac This is the fundamental rule for multiplying polynomials. Every term in the first polynomial must be multiplied by every term in the second polynomial. The FOIL Method for Binomials (a + b)(c + d) = ac + ad + bc + bd This is a systematic process for multiplying two binomials. Multiply the First terms, the Outer terms, the Inner terms, and the Last terms, then combine any like terms.

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Sample Practice Questions

Challenging
A photograph is `(2x - 1)` inches by `(x + 5)` inches. It is placed in a frame that adds a uniform border of 2 inches on all sides. Find a simplified polynomial expression for the area of the frame only.
A.2x^2 + 9x - 5
B.2x^2 + 21x + 27
C.12x + 32
D.12x + 22
Challenging
A painting is `(x + 6)` inches long and `(x - 2)` inches wide. A frame adds a uniform border of 3 inches around the painting. What are the new dimensions of the painting including the frame?
A.Length = (x + 9), Width = (x + 1)
B.Length = (x + 12), Width = (x + 4)
C.Length = (3x + 18), Width = (3x - 6)
D.Length = (x + 9), Width = (x + 4)
Challenging
A rectangle has a length of `(x + 7)` and a width of `(x + 2)`. If the area is 36 square units, what is the value of x?
A.x = 4
B.x = 3
C.x = 1
D.x = 2

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