Re: using excel to solve problem by trial and error...
In A1, put a random value of d as 0.1. Then in B1, put your equation 5*d^4 - 10.29*d^(-1.333), wherein refer d as A1. Then use goal seek function on Tools Menu. First "Set cell" as B1, "To value" as 0.124 and "By Changing Cell" as A1. Excel will do the Trial & Error and will give you the answer in Cell A1.
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Your scientific calculator is unable to solve complex equation with complex coefficients. You should try to solve by hand directly using the quadratic formula or by factoring the polynomial in z failing that, another way would be to set z=x+iy, substitute this for z, carry out the algebra and try to separate real and imaginary parts. But your two equations will constitute a system of two quadratic equations. I am not aware of any general method to solve coupled nonlinear equations. Good luck.
You have to put the equations into matrix form first. To do this, each variable has one column in the first matrix and you fill in the co-efficients for the variables. The second matrix has one column and contains all the numbers.
The best way to solve this is to develop one or more equations and then solve for the unknown numbers.
I solved this problem twice using different sets of equations to make sure I was right, and here is what I found:
1) I used the equations x + y = 623, and x = (2/3)y. In these equations, x is the number of girls and y is the number of boys. Substituting the second equation into the first, I get (2/3)y + y = 623. Adding the left side together I get : (5/3)y = 623. Dividing both sides by (5/3) I get 373.8. This means that x (the number of girls) is 249.2.
2) For the second attempt, I developed the equation: 2x+3x=623. Here 2x is the number of girls, and 3x is the number of boys. Adding the left side I get: 5x = 623. Dividing both sides by 5 I get: x = 124.6. This means that the number of girls (2x) is 249.2. Just like in the first method.
But since you can't have a 1/5 of a girl, the answer must be 249 girls.
Select a blank cell in workbook. Click the function icon located informula bar("fx"). In the popup Insertwindow Select category as ALL.Select the function you want to get help and click on "help on this function " located in the left down page. You can get all the formula help bu using this method.
Put the figure which you have to multiply in cell A1, Put the figure in cell A2 by which you have to multiply by, type =A1*A2 in cell A3. You will get the right answer.
You may substract, multiply or add by this method by appropriate mark in cell A3 in between A1 and A2.