Chapter 9: Problem 1
Multiply 8023 by 4638 using the method of al-Uqlidis?
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Chapter 9: Problem 1
Multiply 8023 by 4638 using the method of al-Uqlidis?
These are the key concepts you need to understand to accurately answer the question.
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Show that \(x^{3}+c x=b x^{2}+d\) is the only one of al-Khayy?mi's cubics that could have three positive solutions. Under what conditions do these three positive solutions exist? How many positive solutions does the equation \(x^{3}+\) \(200 x=20 x^{2}+2000\) have? (The solution of this equation enabled al-Khayy?mi to solve his quadrant problem.)
Use al-T?si's method to solve the spherical triangle with known sides of \(40^{\circ}\) and \(50^{\circ}\) and with the angle between those sides equal to \(25^{\circ}\).
Solve \(\frac{1}{2} x^{2}+5 x=28\) by multiplying first by 2 and then using al- Khw?rizmi's procedure. Similarly, solve \(2 x^{2}+\) \(10 x=48\) by first dividing by 2
Use al-B?r?ni's procedure to determine the qibla for Rome (latitude \(41^{\circ} 53^{\prime} \mathrm{N}\), longitude \(12^{\circ} 30^{\prime} \mathrm{E}\) ).
Al-B?r?ni devised a method for determining the radius \(r\) of the earth by sighting the horizon from the top of a mountain of known height \(h\). That is, al-B?r?ni assumed that one could measure \(\alpha\), the angle of depression from the horizontal at which one sights the apparent horizon (Fig. 9.38). Show that \(r\) is determined by the formula $$ r=\frac{h \cos \alpha}{1-\cos \alpha} $$ Al-B?r?n? performed this measurement in a particular case, determining that \(\alpha=0^{\circ} 34^{\prime}\) as measured from the summit of a mountain of height \(652 ; 3,18\) cubits. Calculate the radius of the earth in cubits. Assuming that a cubit equals \(18^{\prime \prime}\), convert your answer to miles and compare to a modern value. Comment on the efficacy of al-Bir?ni's procedure.
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