22 Tony opened a savings account with the Western Bank.
After one year, the bank paid 6% per annum interest into his account.
The total amount in his account was then £710.20
Work out the amount of money with which Tony opened the account.

answer: 204

step-by-step explanation:

we are told that the revenue is

x⋅(4080−10x)=−10x^2+4080x

this is a quadratic function, so to maximize it we should find the x-value of its vertex. recall that the x-value of the vertex of the parabola ax^2+bx+c is given by the formula −b/2a.

so in this case, we have a=−10 and b=4080, so the x-value of the vertex is

−b/2a= −(4080)/2(−10)=204

m∠a is 90°

m∠b is 40°

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