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Help!:confused:
I do the calcs but my answer can't be right
here's the RX
+1.75-0.50X75
Here's the math steps I'm using;
180-75=105
sin
squared
multiplied
=0.48.......
+ +1.75
=+2.23 @180
that can't be right
what am I missing?
I'm feeling stupid right about now....
You need to subtract .48as it has a negative valueQuote:
Originally Posted by Lori
at what step do i subtract it; subtract it from what? sorry, not a math wiz.
+1Quote:
Originally Posted by Lensman11
In similar problems (plus lens with minus cyl), just realize the answer will never be higher than the plus power.
At what step do i subtract it? subtract it from what? sorry, not a math wiz...Quote:
Originally Posted by Lensman11
Exactly, that's how I knew it is wrong.Quote:
Originally Posted by jefe
Subtract from +1.75 --- BUT --- don't say add or subtract, say combine. Combine two plus numbers, get a bigger number. Combine two minus numbers, get a bigger number (it's minus, but still bigger). Combine a plus and a minus (like your example) and get a smaller number. Will it be plus or minus? Depends on which was bigger to begin with.Quote:
Originally Posted by Lori
Sorry if this just too basic, but it seems to answer your question.
Subtract your answer from the sphere powerQuote:
Originally Posted by finefocus
Actually, you would add it; it's just that you're adding a negative to a positive. Subtracting a negative is the same as adding a positive. That's why add/subtract can confuse people.Quote:
Originally Posted by Lensman11
Actually you always add it algebraic you but she she said her math skills were lacking so a simple answer should suffice.Quote:
Originally Posted by finefocus