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junior college 1 | H1 Maths
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how to find 1st term and ratio? i really appreciate those who kind to help me
Date Posted: 6 years ago
Views: 472
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Part (i) answer:
You can form 2 equations using the information given, using the formula for term of geometric series.
Using simultaneous equations, solve for r.
You will get 2 values of r, one positive and one negative. You need to test both and prove that your answer fulfill all requirements. We know that a must be positive since ar^4 is a positive number, and number x multiplied by a number to its even power will be positive assuming x is positive. If x is negative, it will be negative. Since ar^4 = 8, we can reject the negative solution of r with proof.
From there just plug r into either equation and solve for a.
You can form 2 equations using the information given, using the formula for term of geometric series.
Using simultaneous equations, solve for r.
You will get 2 values of r, one positive and one negative. You need to test both and prove that your answer fulfill all requirements. We know that a must be positive since ar^4 is a positive number, and number x multiplied by a number to its even power will be positive assuming x is positive. If x is negative, it will be negative. Since ar^4 = 8, we can reject the negative solution of r with proof.
From there just plug r into either equation and solve for a.
Date Posted:
6 years ago
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Part ii answer is quite straightforward. Just substitute the real values of r and a into the formula and you will get the answer.
Date Posted:
6 years ago
Clarification: simplify the fraction using conjugate fractions (a+b)(a-b) = (a^2 - b^2)
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