Use logarithms to solve the equation 2^5x = 3^2x+1 , giving the answer correct to 3 significant figures.

Firstly, I would make sure that the student is aware of the basic conept of logarithims and run through the basic "laws" of logarithims to make sure that they have the knowledge they need to answer this type of question. Then I would give them a moment to see if they can spot which law (or laws) can be applied to this equation (bearing in mind there are multiple combinations that can be used). Initially, the logical thing to do is to apply to natural log to the equation(on both sides, needless to say), to come to the equation ln25x=ln32x+1 . After this, you apply the law 'lnxy = ylnx' to both sides. This will lead to the equation being written as: 5xln2=(2x+1)ln3. From here on, it is a simple case of algebra, where the numbers 'ln2' and 'ln3' are treated as constants (an idea which may seem uncomfortable at first, and leads to a few silly mistakes like treating the symbol "ln" as a constant). The answer is 0.866. It is subtly indicated in the question that the answer is likely not to be "pretty" as you are askd to round to three significant figures.

SG

Related Maths A Level answers

All answers ▸

Find the two real roots of the equation x^4 - 5 = 4x^2 . Give the roots in an exact form. [4]


Work out the equation of the normal to the curve y = x^3 + 2x^2 - 5 at the point where x = -2. [5 marks]


The point A lies on the curve with equation y = x^(1/2). The tangent to this curve at A is parallel to the line 3y-2x=1. Find an equation of this tangent at A. (PP JUNE 2015 AQA)  


Solve for x when |x-1|<|2x+3|